Development of TiO2electrical insulation coating on Ag-alloy sheathed Bi2Sr2CaCu2O8−xround-wire

Kandel, Hom; Lü, Jun; Jiang, J.; Chen, P; Matras, M.; Craig, N; Trociewitz, U.P.; Hellstrom, E. E.; Larbalestier, D. C.

doi:10.1088/0953-2048/28/3/035010

Cited by 17 publications

(19 citation statements)

References 27 publications

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“…That Bi-2212 is mechanically-weaker than both REBCO and high-strength Bi-2223 (below) is clear and there are recent attempts to diffusion-bond high-strength materials to aspected Bi-2212 wires to improve the allowable tensile stress from 120 to 150 MPa [39, 40] to more than 400 MPa [40]. Despite the strength- and reaction-difficulties, Bi-2212 has major advantages for high-resolution NMR magnets, and significant progress has been made to address the technological issues [13, 41, 42, 43, 44]. …”

Section: Introductionmentioning

confidence: 99%

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

Godeke

Abraimov

Arroyo

et al. 2017

Supercond. Sci. Technol.

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We performed a feasibility study on a high-strength Bi2−xPbxSr2Ca2Cu3O10−x (Bi-2223) tape conductor for high-field solenoid applications. The investigated conductor, DI-BSCCO Type HT-XX, is a pre-production version of Type HT-NX, which has recently become available from Sumitomo Electric Industries (SEI). It is based on their DI-BSCCO Type H tape, but laminated with a high-strength Ni-alloy. We used stress-strain characterizations, single- and double-bend tests, easy- and hard-way bent coil-turns at various radii, straight and helical samples in up to 31.2 T background field, and small 20-turn coils in up to 17 T background field to systematically determine the electro-mechanical limits in magnet-relevant conditions. In longitudinal tensile tests at 77 K, we found critical stress- and strain-levels of 516 MPa and 0.57%, respectively. In three decidedly different experiments we detected an amplification of the allowable strain with a combination of pure bending and Lorentz loading to ≥ 0.92% (calculated elastically at the outer tape edge). This significant strain level, and the fact that it is multi-filamentary conductor and available in the reacted and insulated state, makes DI-BSCCO HT-NX highly suitable for very high-field solenoids, for which high current densities and therefore high loads are required to retain manageable magnet dimensions.

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Section: Introductionmentioning

confidence: 99%

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

Godeke

Abraimov

Arroyo

et al. 2017

Supercond. Sci. Technol.

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“…The Ag extrusions were irregular in shape and size, and most of them did not penetrate the entire thickness of the insulation layer. Previous studies in our lab showed that cracks and porosity formed in the insulation layer during the sintering of TiO 2 particles [17, 18]. Thus, the Ag extrusions did not crack the insulation, rather they grew into the pre-existing gaps and pores in the TiO 2 insulation.…”

Section: Resultsmentioning

confidence: 76%

“…TiO 2 insulation developed by nGimat and by Kandel et al . appeared to be a successful solution for insulating Bi-2212 [16, 17]. The thin (10–30 μm) TiO 2 coating Kandel et al .…”

Section: Introductionmentioning

confidence: 99%

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Effect of sheath material and reaction overpressure on Ag protrusions into the TiO₂insulation coating of Bi-2212 round wire

Hossain

Jiang

Matras

et al. 2017

IOP Conf. Ser.: Mater. Sci. Eng.

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In order to develop a high current density in coils, Bi-2212 wires must be electrically discrete in tight winding packs. It is vital to use an insulating layer that is thin, fulfils the dielectric requirements, and can survive the heat treatment whose maximum temperature reaches 890 °C. A thin (20–30 µm) ceramic coating could be better as the insulating layer compared to alumino-silicate braided fiber insulation, which is about 100 μm thick and reacts with the Ag sheath during heat treatment, degrading the critical current density (Jc). At present, TiO2 seems to be the most viable ceramic material for such a thin insulation because it is chemically compatible with Ag and Bi-2212 and its sintering temperature is lower than the maximum temperature used for the Bi-2212 heat treatment. However, recent tests of a large Bi-2212 coil insulated only with TiO2 showed severe electrical shorting between the wires after over pressure heat treatment (OPHT). The origin of the shorting was frequent silver extrusions that penetrated the porous TiO2 layer and electrically connected adjacent Bi-2212 wires. To understand the mechanism of this unexpected behaviour, we investigated the effect of sheath material and hydrostatic pressure on the formation of Ag extrusions. We found that Ag extrusions occur only when TiO2-insulated Ag-0.2%Mg sheathed wire (Ag(Mg) wire) undergoes OPHT at 50 bar. No Ag extrusions were observed when the TiO2-insulated Ag(Mg) wire was processed at 1 bar. The TiO2-insulated wires sheathed with pure Ag that underwent 50 bar OPHT were also free from Ag extrusions. A key finding is that the Ag extrusions emanating from the Ag(Mg) sheath actually contain no MgO, suggesting that local depletion of MgO facilitates local, heterogeneous deformation of the sheath under hydrostatic overpressure. Our study also suggests that predensifying the Ag(Mg) wire before insulating it with TiO2 and doing the final OPHT can potentially prevent Ag extrusion.

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“…One critical breakthrough is that using the overpressure (OP) heat treatment (HT), recently developed by our group at the National High Magnetic Field Laboratory (NHMFL), can greatly increase the critical engineering current density ( J e ) of Bi-2212 RW [11]. Furthermore, progress has been achieved in other aspects of Bi-2212 magnet technology [12–15]. In general, Bi-2212 RW conductor has become a competitive conductor candidate for high-field, high homogeneity magnetic field applications, especially for NMR magnets and particle accelerator magnets.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of Potential Heat Treatment Issues of Large Bi-2212 Coils

Chen

Trociewitz

Lü

et al. 2017

IEEE Trans. Appl. Supercond.

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The route to 30 T NMR endorsed by a recent National Academy report clearly still has many challenges to achieve high stability and homogeneous high temperature superconducting (HTS) magnet. As the only HTS conductor with round wire (RW) geometry, Bi2Sr2CaCu2O8-x (Bi-2212) RW conductor is very attractive for NMR magnet applications. At present, an NMR quality demonstration magnet with Bi-2212 RW wound insert coils is under development at the National High Magnetic Field Laboratory (NHMFL). The target of this demonstration magnet is to generate a total field of 23+ T with ppm level homogeneity. Since Bi-2212 coils require Wind-and-React (W&R) technology, our initial major concern was that large Bi-2212 coils might deform during the typical partial melt Bi-2212 heat treatment (HT) due to their large self-weight. To experimentally mimic the HT of large Bi-2212 coil, several small test coils were heat treated under deadweight loads. After 1 bar Bi-2212 full reaction, these coils were characterized in terms of coil geometry, transport critical current properties, oxygenation status and insulation performance. Coil geometry and individual wire shape was in fact not distorted, nor was transport properties degradation was induced by mechanical loading. Uniform oxygen equilibration was achieved in these coils even though they were coated with dense oxide insulation. However, although the TiO2-based insulation coating was well preserved on the wire surface, several coils developed electrical shorts.

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Development of TiO₂electrical insulation coating on Ag-alloy sheathed Bi₂Sr₂CaCu₂O_8−xround-wire

Cited by 17 publications

References 27 publications

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

Effect of sheath material and reaction overpressure on Ag protrusions into the TiO₂insulation coating of Bi-2212 round wire

Experimental Study of Potential Heat Treatment Issues of Large Bi-2212 Coils

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Development of TiO2electrical insulation coating on Ag-alloy sheathed Bi2Sr2CaCu2O8−xround-wire

Cited by 17 publications

References 27 publications

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

Effect of sheath material and reaction overpressure on Ag protrusions into the TiO2insulation coating of Bi-2212 round wire

Experimental Study of Potential Heat Treatment Issues of Large Bi-2212 Coils

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Product

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Development of TiO₂electrical insulation coating on Ag-alloy sheathed Bi₂Sr₂CaCu₂O_8−xround-wire

Effect of sheath material and reaction overpressure on Ag protrusions into the TiO₂insulation coating of Bi-2212 round wire