LOCAL PHASE EVOLUTION IN (PB/BI)(2)SR2CA2CU3OX TAPES

The phase evolution has been measured locally from the core-sheath interface to the core-centre of(Pb/Bi)2223 tapes sintered for up to 350 h. The rate of the phase conversion is found to be much faster at the interface than at the centre. For example, in a tape sintered at 832 degrees C in air for 30 h, the percentage of 2223 phase is similar to 90% at the interface compared with similar to 27% at the centre. Consequently, there is a 2223 phase gradient from the interface to the centre of the core, even after a long sintering time. There appears to be an associated gradient in the grain size and Vicker's microhardness across the thickness of the core. The influence of the silver sheath on the phase conversion in half-peeled tapes has also been studied. The half-peeled tapes were made by removing one side of the silver sheath of the normal (Pb/Bi)2223 tape before sintering.