POWDER COMPACTION CHARACTERISTICS AND TUBE DIMENSIONS IN PIT FABRICATION OF AG BPSCCO SUPERCONDUCTING TAPES/

Density variations of the superconductor core during the powder-in-tub e (PIT) fabrication of Ag/BPSCCO monolayer tapes have been studied. Th e PIT procedure involved steps such as filling the tubes with precurso r powder, rich in 2212 phase, with packing densities in the range 20-5 5% of theoretical density, groove rolling, flat rolling and finally a four-stage repeated rolling-annealing cycle. The two types of precurso r powders used in this study were prepared by a conventional ceramic r oute and an amorphous acrylate route (AR). The core density was found to saturate after a few passes of just groove rolling for both powders . However, better compaction was achieved by rolling for the AR powder which also exhibited a better uniaxial compaction response. A further increase in core density was observed only during the final annealing step. Based on the experimentally observed constancy of core density through most of the mechanical working steps, a relation connecting si lver sheath thickness, total thickness and cross-section ratio at satu ration of compaction has been worked out. Apart from explaining the in fluence of starting packing density and compaction response of powder in determining the sheath thickness of the final tapes, the relationsh ip was found to be useful in choosing the starting packing density app ropriate to the silver tube dimensions and prevailing rolling conditio ns.