Local phase evolution in (Pb/Bi)2Sr2Ca2Cu3Ox tapes

Monocore (Bi,Pb)-2223 tapes have been made by a sequence of thermomechanical steps involving two-axial and eccentric rolling and annealing for between 20 and 100 h. The purpose of this treatment was to differentiate tapes in texturization degree and phase content allowing for texture and phase development monitoring during the thermomechanical treatment. Texture degrees, phase content and purity were measured by x-ray diffraction (XRD). Results obtained have confirmed different susceptibility to texturization between the two main phases (`high' for 2223 and `weak' for 2212) and have visualized differences between ceramic at the Ag interface versus core centre. Evidence of a c -axis constant decrease, 2223-phase content and purity increase, higher texturization degree and smaller volume of secondary phases has been found and demonstrated for this interfacial layer. Observed properties are discussed and related to process parameters and the critical current density Jc in final tapes.

Section: Resultssupporting

confidence: 72%

“…Distribution of phase purity and content as well as texture distribution across the core thickness were studied on tapes from which the Ag sheath was etched away and then thin layers of the broad face of the ceramic were progressively removed by careful polishing. This technique has been already successfully applied in other works [10,11].…”

Section: Methodsmentioning

confidence: 96%

Distribution of inhomogeneities across the ceramic core in monocore (Bi,Pb)-2223/Ag tapes

Pachla

Diduszko

Kòváč

et al. 2000

“…Correspondingly, flux patterns obtained by magneto-optical (MO) imaging in asprepared (rolled) Bi-2223 tapes are found to be nearly homogeneous, and governed essentially by the large intergranular currents. Weak disturbances of the ideal homogeneous flux distribution are caused by cracks which are not healed during the preparation (typically caused by additional pressing [3]) and by foreign phases and/or silver particles found inside the tape core [4].…”

Section: Introductionmentioning

confidence: 99%

Bending of silver-sheathed (Bi,Pb)-2223 tapes investigated by magneto-optical flux visualization

Koblischka

Johansen

Bratsberg

1997

The effect of bending on silver-sheathed Bi-2223 tape is investigated by means of magneto-optical (MO) visualization of flux distributions. One single piece of rolled tape is used throughout all experiments starting from as-prepared, and subsequently the tape is bent to 4 mm diameter and then down to 1 mm diameter in 1 mm steps. Flux patterns are visualized using an intact tape, i.e. the visualization is done through the silver sheath after removing the bending strain. It is shown that bending of the tape causes a series of cracks running perpendicular to the tape axis (rolling direction). This crack pattern remains practically unchanged down to 1 mm bending diameter. The flux penetration changes from nearly homogeneous (as-prepared) to entirely crack-governed. Vortices are found to penetrate the tape preferentially along the cracks and from there into the remaining bulk. In bent samples, a very homogeneous flux distribution is observed when the external field is decreased after having reached the full-penetration field. A further decrease of the field forces vortices to leave the sample along the cracks, and trapped vortices remain within the Bi-2223 grains (grain clusters). With each step of bending, the values for the first flux penetration and full-penetration field are decreased. The observations of flux patterns at 1 mm bending diameter clearly demonstrate that intergranular currents are still flowing in the sample. Our observations demonstrate the capability of the MO technique for non-destructive testing of superconducting tapes.

“…In pressed tapes the microcracks run along the tape, parallel to the current flow direction, but in rolled tapes they run transverse to the current flow, lowering the longitudinal transport current I c . There is considerable evidence that texture development is more pronounced at the interface between the ceramic core and the silver sheath [2,3]. Close to the silver sheath the conversion to the BSCCO-2223 is more complete and the grains are larger and more highly aligned; consequently the critical current density is highest close to the silver sheath and at the edges of the ceramic core.…”

Section: Introductionmentioning

confidence: 99%

Self-field AC losses and critical currents in multi-tube Ag - Bi-2223 conductors

Ciszek

Ashworth

James

et al. 1996

The purpose of this work was to investigate the influence of different technological treatments of silver sheathed Bi-2223 tapes on the critical current density and the AC transport losses. The tapes were produced using the 'tube-in-tube' technique, by including a silver rod in the centre of the superconducting powder during packing of the silver tube. The aim of the process is to increase the silver to superconductor surface area and thus also the alignment at the centre of the conductor ceramic core. AC transport losses were measured by means of an electrical method using sinusoidally varying currents in the frequency range 30-180 Hz. In this range the power losses are hysteretic. The measured variation in losses from those predicted by a critical state model is attributed to the complex geometry of superconducting regions existing in these tapes.