Modified heat-treatment process of precursor powders for Bi-2212 tapes preparation

Hao, Qingbin; Li, C.S.; Zhang, S.N.; Bai, Li Feng; Ma, Xinkai; Feng, Jin

doi:10.1016/j.phpro.2012.03.462

Cited by 4 publications

(1 citation statement)

References 6 publications

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“…In the case of Bi-2212 tape conductor, one of major causes of low J E in long-length Bi-2212 was suggested to be high internal gas pressures at high temperatures [19][20][21][22][23]. Internal gases may include residual air and humidity present in as-drawn wires, gases released as a result of contaminants adsorbed on powder surfaces [24] and solid remnants in powder gasifying upon heating. Contaminants and gas impurities may include hydrates, hydroxides, carbonates [25], nitrates, and residues such as wire drawing lubricants (hydrocarbons); they transform to gases (H 2 O, CO 2 , or NO 2 ) upon heating.…”

Section: Introductionmentioning

confidence: 99%

Role of internal gases and creep of Ag in controlling the critical current density of Ag-sheathed Bi2Sr2CaCu2Ox wires

Shen

Ghosh

Cooley

et al. 2013

Journal of Applied Physics

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High engineering critical current density J E of >500 A/mm 2 at 20 T and 4.2 K can be regularly achieved in Ag-sheathed multifilamentary Bi 2 Sr 2 CaCu 2 O x (Bi-2212) round wire when the sample length is several centimeters. However, J E (20 T) in Bi-2212 wires of several meters length, as well as longer pieces wound in coils, rarely exceeds 200 A/mm 2 . Moreover, long-length wires often exhibit signs of Bi-2212 leakage after melt processing that are rarely found in short, open-end samples. We studied the length dependence of J E of state-of-the-art powder-in-tube (PIT) Bi-2212 wires and gases released by them during melt processing using mass spectroscopy, confirming that J E degradation with length is due to wire swelling produced by high internal gas pressures at elevated temperatures [1,2]. We further modeled the gas transport in Bi-2212 wires and examined the wire expansion at critical stages of the melt processing of as-drawn PIT wires and the wires that received a degassing treatment or a colddensification treatment before melt processing. These investigations showed that internal gas pressure in long-length wires drives creep of the Ag sheath during the heat treatment, causing wire to expand, lowering the density of Bi-2212 filaments, and therefore degrading the wire J E ; the creep rupture of silver sheath naturally leads to the leakage of Bi-2212 liquid. Our work shows that proper control of such creep is the key to preventing Bi-2212 leakage and achieving high J E in long-length Bi-2212 conductors and coils.

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