Phase chemistry and microstructure evolution in silver-clad (Bi(2-x)Pb(x))Sr2Ca2Cu3O(y) filaments

摘要

The reaction kinetics and mechanism that control the conversion of (Bi,Pb)(sub 2)Sr(sub 2)CaCu(sub 2)O(sub z) (Bi-2212) + alkaline earth cuporates to (Bi, Pb)(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub y) (Bi-2223) in silver-clad wires were investigated as a function of equilibration temperature and time at a fixed oxygen partial pressure (7.5% O(sub 2)). Measured values for the fractional conversion of Bi-2223 versus time have been evaluated based on the Avrami equation. SEM and TEM studies of partially and fully converted wires have revealed that (1) the growth of Bi-2223 is two-dimensional and controlled by a diffusion process, (2) liquid phases are present during part of the Bi-2212 (minus)> Bi-2212 conversion, and (3) segregation of the second phases occurs in early time domains of the reaction.