CHEMICAL DIFFUSION IN THE BI, SR, CA, CU O SYSTEM/

Monodimensional diffusion measurements have been used to characterise the solid state reactivity in the Ca, Sr, Cu, Bi/O system at 750 degre es C under pure oxygen flux (1 atm). The investigated couples are: (1) Bi2O3-CaCO3; (2) CaCO3-CuO; (3) CaCO3-SrCO3; (4) Sr2Bi2O5-CaCO3; (5) CaBi2O4-SrCO3; (6) CaBi2O4-CuO; (7) CuBi2O4-CaCO3; (8) CaBi2O4-SrCuO2. The paper reports the phase nature and composition of the solid produ cts formed by the various couples, as well as their rates of formation . In most cases, reaction mechanisms and rate-controlling species have been determined. The paper discusses the problem of finding a clean s olid state path towards a pure ''2212'' phase, i.e. a suitable sequenc e of solid state reactions such that each reaction gives a single phas e product. The results show that a reaction path of this kind is not a vailable under the selected external conditions (750 degrees C, pure o xygen environment at 1 atm, carbonate precursors, and 2:2:1:2 Bi:Sr:Ca :Cu ratio).