Investigation of a multi-set-point first heat treatment methodology for the silver-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox composite conductor

A new type of first heat treatment procedure for the silver-sheathed (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x composite conductor (Ag/Bi-2223) has been investigated. This new procedure consists of using multiple oxygen partial pressure/temperature set point conditions that are systematically varied during the course of the first heat treatment. The present embodiment of this procedure (referred to as thermal slide heat treatment) involves the use of three specific set point conditions (21.0% O 2 /835 °C, 7.5% O 2 /825 °C and 4.0% O 2 /815 °C) appropriately sequenced and tuned to specific time intervals. Application of this procedure as a first heat treatment for powder-in-tube-type Ag/Bi-2223 composite wire specimens was found to produce a minimal amount (<8 area% as seen in cross section views of transverse mounted specimens) of finely divided nonsuperconducting secondary phases in the Bi-2223 filament cores. Also, a direct correlation was observed between the amount of nonsuperconducting secondary phase contained in the Ag/Bi-2223 specimens at the end of the first heat treatment and the performance (in terms of J C ) of the fully processed specimen.