We studied the influence of using different powders and several additives on the shaping process and critical current density of sintered bulk YBa2Cu3OX. It was found that all additives used facilitated the shaping process. Silver and most organic additives influenced the critical current density only little, Zinc reduced it to zero, but an ethylenebisstearoylamide compound doubled the critical current density as compared to samples without additives

Hemmes, H.

Hoogendam, P.

Klundert, L.J.M. van de

Kolster, B.H.

Kuper, A.R.

English

van de Klundert, L.J.M.

University of Twente Research Information

physica B 165&166 (1990) 1385-1386North-HollandTHE INFLUENCE OF ADDITIVES ON THE CURRENT CARRYING CAPACITY OF BULK YBa2Cu30XA.R. Kuper ., P. Hoogendam +, H. Hemmes ., B.H. Kolster + and L.J.M. van de Klundert •• University of Twente, Applied Physics, P.O. Box 217, NL-7500 AE Enschede, the Netherlands+ Foundation for Advanced Metals Science, P.O. Box 8039, NL-7550 KA Hengelo, the NetherlandsWe studied the influence of using different powders and several additives on the shaping processand critical current density of sintered bulk YBa2Cu30x' It was found that all additives usedfacilitated the shaping process. Silver and most organic additives influenced the critical cur-rent density only little, Zinc reduced it to zero, but an ethylenebisstearoylamide compound dou-bled the critical current density as compared to samples without additives.1. INTRODUCTIONFor sintered bulk YBa2Cu30x the critical cur-rent density typically is a few A/mm2 • For ap-plications, this will have to be at least oneorder of magnitude larger. This has been achie-ved by, for instance, melt processing (1,2).This technique, however, only improves the cur-rent carrying capacity on a small length scale.The aim of our work was to improve the currentcarrying capacity of bulk YBa2Cu30x by usingadditives.nic compounds. As a reference we also preparedrings without any additives. All rings receivedthe same heat treatment in 1 bar of flowing oxy-gen: 5 hours at 500 °C to remove the binder, 10hours at 925 °C for sintering and finally 10hours at 400 °C to restore the oxygen contents.3. RESULTSRings made from citrate powder without anyadditives have a critical current density of ~2Almm2. A typical hysterisis curve of the genera-ted current as a function of the applied magne-tic field, measured at 77 K, is shown in figure1. The curve contains a small contribution pro-portional to the applied field because of animperfect compensation of the pick up coils. Thecritical current determined from this curve is 7A, corresponding to a current density of 1.75A/mm2 •FIGURE 1. Hysterisis curve of thecurrent against the applied magnetiction for a ring prepared from citratewithout additives.inducedinduc-powder5oBa ( mT )-5Of---~""-----t------= "'-I5-5<........2. EXPERIMENTALFor the determination of the critical currentwe used an inductive technique. By applying anAC field a current is induced in a ring shapedYBa2Cu30x sample. The induced current can bemeasured using pickup coils (3). This techniquehas the advantage that a large current can begenerated (presently up to 10 kA) without havingto make contacts to the sample. The main disad-vantage is that the sample has to be ring sha-ped. The rings are made by uniaxially compres-sing YBa2Cu30x powder in a mold, followed bycold isostatic pressing. The rings typicallyhave an inner(outer) diameter of 25(29) mm and athickness of 2 mm. The current carrying crosssection is therefore 4 mm2.The mechanical and superconductive propertiesof the resulting rings depend strongly on theshape and size of the powder used. We have usedpowders prepared by the standard solid statereaction method (standard powder), with a grainsize of the order of a hundred ~m. We also usedpowders prepared by the citrate synthesis andpyrolysis method (citrate powder) (4) with atypical grain size of less than 10 ~m and anirregular shape.It was found that it is difficult to form amechanically stable ring using the citrate pow-der because it is very fine. This problem can besolved by mixing the YBa2Cu30x powder with ano-ther powder that acts as a binder. For this pur-pose we have used Zinc, Silver and several orga-0921-4526/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)1386 A.R. Kuper, P. Hoogendam, H. Hemmes, B.H. Kolster, L.J.M. van de KlundertFigure 2 shows the induced current in thesample with Zinc added, measured at 77 K. Theshape of the curve is completely different fromthat in fig. 1. Also, because of the small sig-nal, the imperfect compensation of the pick upcoils has a much larger influence. We concludefrom this figure that the sample is not super-conducting and has therefore a zero criticalcurrent.Figure 3 shows the hysteris curve of a samplewith ethylenebisstearoylamide added. The curvehas the same form as in fig. 1, but the currentis much larger: 20 A, corresponding to a currentdensity of 5 Almm2 . The largest critical currentdensity obtained with this additive is 10 A/mm2 ..4< 0~....-.4-5 o 54. DISCUSSIONZn has a very high vapor pressure and wasthought to evaporate before the sinter processstarted. It showed however that Zn reacts withoxygen, released from the Cu-O planes, formingZnO. As a result the critical current densitywas reduced to zero. All organic binders decom-posed before the sinter process started and didnot influence the critical current density. How-ever, for the ethylenebisstearoylamide compoundthe critical current density doubled as comparedto the reference samples. Finally, adding Silverto the YBa2Cu30x powder has little influence onthe critical current.Ba ( mT )FIGURE 2. Hysterisis curve of the inducedcurrent against the applied magnetic induc-tion for a ring prepared from citrate powderwith Zinc added.5. CONCLUSIONSWe have found that ring made from citratepowder have a larger critical current densitythan those made from standard powder. Further-more, additives have shown to be very helpfullin the shaping process and do not necessarilyhave a negative effect on the critical currentdensity in bulk YBa2Cu30x ' Adding ethylenebis-stearoylamide doubled the critical currentdensity.FIGURE 3. Hysterisis curve of the inducedcurrent against the applied magnetic induc-tion for a ring prepared from citrate powderwith ethylenebisstearoylamide added.<-10 o 10ACKNOWLEDGEMENTSWe would like to acknowlegde the NationalResearch Program for High Temperature Supercon-ductors (NOP-HTc) for their financial support.REFERENCES(1) S. Jin, T.H. Tiefel, R.C. Sherwood, M.E.Davis, R.B. van Dover, G.W. Kammlott, R.A.Fastnacht, and H.D. Keith, Appl. Phys.Lett. 52 (1988) 2074(2) K. Salama, V. Selvamancickam, L. Gao and K.Sun, Appl Phys. Lett. 54 (1989) 2352(3) L.J.M. van de Klundert, P. Out, B. tenHaken, G.J.M. Velders, D.H.A. Blank andW.S.J. Uijttewaal, in: Proceedings of theEuropean Workshop on HIGH Te SUPERCONDUC-TORS AND POTENTIAL APPLICATIONS, 1-3 July,1987(4) D.H.A. Blank, H. Kruidhof and J. Flokstra,J. Phys. D: Appl. Phys. 21 (1988) 226

The influence of additives on the current carrying capacity of bulk YBa2Cu3OX

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The influence of additives on the current carrying capacity of bulk YBa2Cu3OX

Hemmes, Herman K.

The influence of additives on the current carrying capacity of bulk YBa2Cu3Ox

https://doi.org/10.1016/S0921-4526(09)80278-0

The influence of additives on the current carrying capacity of bulk YBa2Cu3OX

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