Preferred orientation of BSCCO via centrifugal slip casting
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Preferred orientation of BSCCO via centrifugal slip casting Greg Steinlage, Ryan Roeder, Kevin Trumble, and Keith Bowman School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907-1289
Shi Li and Mike McElfresh Physics Department, Purdue University, West Lafayette, Indiana 47907-1289 (Received 19 July 1993; accepted 15 December 1993)
Due to the highly anisotropic properties of BSCCO superconductors, the bulk properties of these materials can be greatly affected by preferential orientation. Substantial c-axis orientation normal to the desired direction of current flow has been demonstrated by centrifugally slip casting lead-doped BSCCO-2223. The strong preferred orientation developed in the centrifugally slip-cast material demonstrates high critical current potential.
Limitations to attaining high critical current density (Jc) in bulk polycrystalline high-J c superconductors include crystallographic Jc anisotropy,1 superconducting weak links at grain boundaries,2 and flux line depinning above the irreversibility line.3 Many of these materials exhibit anisometric grains which can result in low bulk density, further limiting Jc. Texturing anisometric high-J c superconductors provides a means for crystallographic alignment, suppressing weak link effects, and increasing bulk density, thereby improving superconducting properties. Many researchers have focused on manufacturing techniques geared toward developing preferred orientation in superconducting materials.4 Most of these methods are complex and employ liquid phase or powder processes that have limited potential for introducing preferred orientation in bulk components.5'6 Melt quenching typically produces a thin amorphous layer which must then be annealed to induce crystallization and grain orientation.5'7 The popular powder-in-tube process involves multiple rolling and annealing steps to produce textured wires or tapes.8 Rolling and other deformation processes induce high stresses, and may rely on the fracturing of particles to induce texture. Traditional powder routes for producing oriented microstructures in materials containing anisometric grains include cold pressing,9 tape casting,7 and conventional slip casting.1 Cold pressing of high aspect ratio powders induces texture by forcing the particles to deform, fracture, and/or rotate so that the long direction of the particles is perpendicular to the pressing direction. In tape casting, shearing action aligns the suspended anisometric particles within the slip.7 Conventional slip casting offers two mechanisms for producing texture. Plate-like particles tend to settle from suspension with J. Mater. Res., Vol. 9, No. 4, Apr 1994 http://journals.cambridge.org
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their long dimensions perpendicular to the settling direction1 and capillary fluid flow around settled particles further aids in alignment. Slip casting can produce complex shapes and may not necessitate multiple heat treatments or subsequent deformation processing. Centrifugal slip casting of anisometric supe
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