Effect of resolidification conditions on Bi2Sr 2CaCu2OX/Ag/AgMg coil performance

Xiaotao T. Liu, William T. Nachtrab, Terry Wong, Justin Schwartz

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

The performance of Bi2Sr2CaCu2 O x (Bi2212) wires is very sensitive to the heat treatment conditions, and in particular to the conditions immediately after partial-melting. In this paper, the effect of solidification conditions on Bi2212/Ag/AgMg coil performance is investigated using a split melt process. After partial melting, Bi2212 is first cooled with a relatively fast cooling rate, 10°C/hr, for a short time until reaching "Ti" and subsequently by a slower cooling rate, 2.5°C/hr, for a much longer period of time. Here we study the effects of varying. With decreasing "11, the overall effective cooling rate during resolidifi- cation, particularly the initial stage of resolidification, is increased. As a result, the Bi2212 grain size and the bridges between filaments are inhibited. For short witness samples heat treated with the coils, the transport current and the connectivity decrease with decreasing. A similar tendency is observed in coils, however the coils also show inhomogeneous performance within the conductor. In coils the end sections have higher transport critical current and better connectivity than the middle sections. With decreasing the difference between end sections and middle sections also decreases. Microanalysis shows that with the insulation on the conductor (both witness samples and short samples cut from coil sections) during heat treatment, increased copper-free phases are found in the Bi2212 filaments as compared to the witness samples heat treated without insulation. In short samples cut from coils, microanalysis also shows an increase in the number of outer filaments that are lost. EDS analysis indicates that Ag and Cu react with the insulation fiber. The Cu diffuses through the Ag sheath and reacts with the insulation fiber, leading to Cu deficiency in the filaments.

Original languageEnglish (US)
Article number5067074
Pages (from-to)2232-2236
Number of pages5
JournalIEEE Transactions on Applied Superconductivity
Volume19
Issue number3
DOIs
StatePublished - Jun 1 2009

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering

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