With the growing potential for use of Bi-2212 powders in high temperature superconducting applications, it is important to understand the processing characteristics of the material. To meet this need, the present work established the relationship between confining pressure and green density for powders of different particle sizes and morphologies. Mechanical properties, including elastic and plastic behavior, of the resulting green compacts were also measured as a function of relative density. Particle size and size distribution are shown to have a significant impact on the properties of interest. The implications of such findings are discussed with respect to the powder-in-tube process for making high temperature superconducting wire and tape.
Sintering of pure SnO 2 to high densities is difficult due to its high vapor pressure, and hence, additives are typically used to enhance densification. In this study, the effects of two lithium compounds, LiF and LiNO 3 , on the densification behavior of SnO 2 were evaluated. While LiF resulted in only a modest improvement in densification, LiNO 3 additions resulted in densities of 5=95% theoretical at 1500 °C in air. Thermal, x-ray, and SEM/TEM microstructural analyses indicated no liquid phase formation. From these studies we attribute the enhanced sintering behavior to the ionic-compensation of Li + as an acceptor dopant, i.e., 3[Li' s '^] = 2[Vo], which in turn increased the diffusivity of oxygen.
In this study, we fabricated monocore tapes of Bi-2212 imbedded in a silver sheath. We then fabricated multi-filamentary conductors by laminating several monocore tapes using a turkshead roller and a heat treatment. The conductors exhibit satisfactory structural integrity, and for short lengths, the critical current density at 4.2 K was as high as 93,000 A/cm* for a 7-filament conductor in a 5 T field perpendicular to the conductor surface.
The powder-in-tube process has been widely used to fabricate long lengths of Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) superconducting wires and tapes. However, there is not a good understanding of the processing variables involved in the wire-drawing process. Recent studies indicated that powder characteristics, such as particle size distribution and morphology, had a significant effect on the consolidation behaviour of Bi-2212 green compacts. In this investigation, silver-clad Bi-2212 composite wires containing powders of two different particle sizes were fabricated. The effects of initial packing density and sheath thickness on the characteristics of the wires, including elongation, silver:core ratio and relative core density, were investigated. It is observed that coarse powders with a wide particle size distribution produce wires with higher core density and a moderate benefit is obtained from higher initial powder packing density.
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