Kinetic study of the formation of Bi_1.8Pb_0.2Sr₂Ca₂Cu₃ O_x ceramic superconductor

The compound under investigation was prepared with the nominal composition Bi_1.8Pb_0.2Sr₂Ca₂Cu₃ O_x through solid-state reaction starting from Bi₂O₃, PbO, SrCO₃, CaCO₃ and CuO powders. Reactions among components were investigated by thermogravimetric and differential thermal analysis in the temperature range 700-850 °C. Reaction kinetics for the solid-state synthesis of Bi_1.8Pb_0.2Sr₂Ca₂Cu₃ O_x (compound A) were evaluated according to the mathematical relationships derived theoretically for phenomenological models and were compared with those for a Bi_1.8Pb_0.2Sr₂Cu₃O_x mixture (compound B), in order to formulate a correlation among the starting nominal compositions, the kinetic results and a phenomenological model for the solid-state reaction. A second-order classical model provides a reaction kinetics suitable for describing the process at temperatures lower than 770 °C for system A and at temperatures lower than ≈815 °C for system B. At higher temperatures a three-dimensional diffusion model fits the data for both systems. Crystalline phases and microstructural features of samples derived from the thermal treatments were analyzed.