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Title: A study of the effects of the processing parameters on the transport Jc of (Pb,Bi)2223 superconducting tapes
Author: Spiller, Darren Michael
ISNI:       0000 0001 3475 3367
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1997
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High current applications of (Pb,Bi)2223 tapes demand a high transport critical current density (Jc) and due to the intrinsic magnetic field associated with high currents the transport Jc of the conductors must have good Jc-B characteristics. The tapes must also be mechanically stable to withstand the stresses impaired during conductor preparation and during operation. In this study processing parameters were investigated in order to improve the transport Jc(77K), Jc-B characteristics and handling properties of the (Pb,Bi)2223 tapes produced. The effects of sintering temperature on the formation of the (Pb,Bi)2223 phase and the transport Jc was studied. This study revealed a suitable window of preparation of (Pb,Bi)2223 tapes of 830°C-840°C in air which resulted in a transport Jc of 1.8 x 104Acm⁻². The effects of the intermediate mechanical treatment of the tapes during preparation was studied to clarify the difference in transport Jc of tapes prepared with intermediate cold rolling and pressing. This difference did not appear to be as large as that reported by other authors. The influence on the (Pb,Bi)2223 formation and the transport Jc was studied for heating rates of 2Kh⁻¹, 5Kh⁻¹, 20Kh⁻¹ and 40Kh⁻¹. The (Pb,Bi)2223 phase was found to form quickest for the slower heating rates (2Kh⁻¹ and 5Kh⁻¹) with a delay in the initial (Pb,Bi)2223 formation for tapes heated at 20Kh⁻¹ and 40Kh⁻¹. At slow heating rates, e.g. 5Kh⁻¹ a relatively large fraction of 2201 present in the core after 30h at 830°C and 840°C which appears to have had a detrimental effect on the magnitude of the transport Jc. For the conditions used in this study the most successful heating rate was 20Kh⁻¹ to 840°C which resulted in a self field Jc of 1.2 x 104Acm⁻². The use of a silver alloy sheath material (Ag and (0.5% Ni,Mg)) on the transport Jc was studied with respect to the sintering time. The use of a silver alloy was found to improve the magnitude of the self field transport Jc and reduced the time required to produce the peak Jc at 830°C (JcPeak(Ag)=7500Acm⁻² after 250h, JcPeak(Alloy)=14250Acm⁻² after 130h). A further consequence of the alloy sheath was an improvement in the Jc-B characteristics for applied fields 0 < B < 0.5T.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available