Microstructural evolution at the initial stages of annealing in a Bi-2223 multifilament tape

Abstract

The microstructural evolution at the initial stage of annealing in a multifilament Bi-2223Bi- (2223 tape is studied in quenched samples using XRD, SEM and EDS. The annealing was carried out at 830 • C under reduced oxygen partial pressure. Samples were quenched in air upon reaching 830 • C, as well as after 1, 2, 5, 10, 30 and 52 h at 830 • C. It was found that the initial liquid formation was associated with alkaline-earth cuprate (AEC) particles such as (Ca,Sr) 14 Cu 24 O z and (Ca,Sr) 2 CuO 3 . The liquid is rich of Pb and the AEC particles dissolve and supply Cu and Ca into the liquid through direct contact. The 2223 kinetics are well correlated with the structural parameters of liquid and AEC particles. During the first hour the liquid activity is confined to the neighbourhood of AEC particles and the rate of 2223 formation is very low. Between 2 and 10 h the liquid amount increases and the size (measured in tape plane) is comparable with the particle spacing indicating a liquid activity on an overall scale and sufficient feeding of Cu and Ca. Consequently, the 2223 develops at a fast rate. After 10 h the liquid amount is decreased, the particle spacing is far larger than the liquid size and the rate of 2223 formation slows down. The early 2223 forms as precipitates in the structure. The possible formation mechanisms are discussed.

Critical current enhancement in Bi-2223/Ag superconducting tapes by controlling its first sintering process

“…Samples treated at 830 • C have faster formation speed than that of being treated at 840 • C. Meanwhile, the evolution of the liquid phase fraction during the sintering shows an interesting feature. During the first 10 h, its volume fraction increases with the sintering time and reaches a maximum at 10 h and then slowly decreases, which is in good agreement with the results obtained by Liu et al [7] and Giannini et al [13]. We ascribe this to the fact that Bi-2212 phase, which is the main source of liquid phase, decreases rapidly during the fast formation of Bi-2223 during the first sintering process [14].…”

“…For realization of such applications, much effort has been made in order to further improve the critical current density of the Bi-2223/Ag tapes [1][2][3][4][5]. It is widely accepted that one important factor for the successful control of the phase formation and the microstructure is the first sintering process of the tapes, which seems to be a critical step for the formation of a desirable final structure [5][6][7][8][9]. During the first sintering process, a majority of the precursor powder is converted into the superconducting Bi-2223 phase.…”

Influence of SrF2 on the Formation, Microstructure and Critical Temperature of (Bi,Pb)2Sr2Ca2Cu3O10 Polycrystalline Samples

“…This hypothesis is based Fig. 5 a- [37] showing that the grain size of the non-superconducting phases regularly increases with time as the Bi2223 phase forms from calcinated precursor powders. Increasing the sintering temperature for a fixed nominal composition promotes in general, the growth of non-superconducting particles due to the availability of a higher amount of transient liquid phase [38].…”

Quantitative Electron Microscopy of (Bi,Pb)2Sr2Ca2Cu3O10+δ/Ag Multifilament Tapes During Initial Stages of Annealing

“…Optimization of the physical properties of 2223 tapes strongly depends on the microstructure and the understanding of the (Bi,Pb) 2 Sr 2 CaCu 2 O 8+δ (2212) to 2223 transformation, which starts taking place during the initial stages of annealing. Unfortunately, detailed studies on the microstructural and compositional evolution during this stage are limited 4,5 …”

“…The appearance of a Pb‐rich liquid during the phase transformation has been studied by scanning electron microscopy (SEM) in combination with energy‐dispersive X‐ray spectroscopy (EDX) 4 but the spatial resolution of this technique is limited. In the present work, energy‐filtered transmission electron microscopy (EFTEM) and quantitative EDX are used in combination with conventional transmission electron microscopy (TEM) and high‐resolution transmission electron microscopy (HREM).…”