Kinetic formation of (Bi, Pb)-2223 compound during the last stage of a multi-step thermal preparation process

A kinetic study of the (Bi,Pb)-2223 phase formation has been performed through a two-cycles annealing process at a temperature of 835°C by X-ray diffraction and SEM observations. Samples were Pb-doped (part 0.4 of Bi substituted by Pb) during the first thermal cycle. A second substantial addition of up to 10% excess of PbO in weight was added at the beginning of the second thermal cycle. PbO addition was shown to be more effective during the second cycle. Using the Avrami equation, a kinetic study of the (Bi,Pb)-2223 phase formation mechanism was conducted. The reaction order, n has been shown to depend on PbO excess and thus the (Bi,Pb)-2223 formation mechanism. With lower excess of PbO (0% and 4%), n is about 0.5 and the related formation mechanism corresponds to the thickening of plates after their edges have been impinged. With higher excess of PbO (10%), n is about 2,2 and the related mechanism corresponds to the initial growth of particles nucleated at a constant rate.