Mass density evolution during manufacturing of Ag-sheathed BPSCCO tapes

The mass density of superconducting (bismuth, lead)-strontium-calcium-copper-oxide (PBSCCO) cores of silver-sheathed tapes, subject to different states of cold working and thermal treatment, has been determined taking advantage of a modified hydrostatic weighing. It turned out that the densification was more effective the smaller the initial density of the parent material. A core density of about 5 g cm-3 was attained, but could not be exceeded, independent of the deformation method and core density prior to deformation. When starting with high initial densities, drawing even reduced the core density. The density drop increased with reduced diameter reduction per drawing step, whereas rolling improved the core density. Heat treatment (reacting from the 2212 to the 2223 phase) resulted in a small loss of relative density, which raised with increasing core thickness. Nevertheless there is a positive correlation between densities before and after heat treatment. It is therefore important to obtain optimum core densities during the final steps of cold working. (author)