Effects of the reaction time on various properties of tapes

The mechanisms leading to a maximum of as a function of reaction time in monofilamentary tapes are investigated. Various properties of tapes previously reacted for 40 h in air at , rolled and submitted to additional reaction during times varying from 40 to 240 h were measured. The evolution of the morphology, phase assembly, stoichiometry, weight, critical temperature, critical current and irreversibility line is described. XRD and SEM analysis reveal no decomposition of the Bi(2223) phase and no noticeable grain growth after the 40 h additional time. Pb losses up to 40% were detected by means of thermogravimetry and EDX as function of reaction time, while an increase of from 107.25 to 109 K was observed. On transport and magnetic measurements, it is found that the observed maximum of at about 180 h is the result of two competing effects: (a) the improvement of the quality of grain boundaries and (b) the decrease of the pinning efficiency in the grains.