REACTIVITY OF THE BI, SR, CA, CU OXALATE POWDERS USED IN BSCCO PREPARATION

The solution chemistry of oxalate coprecipitation of Bi, Si, Ca, Cu ha s frequently! been used in the synthesis of Bi-based ceramic systems, although there are different opinions referring to some major aspects, such as coprecipitation pH and precipitating agent. In the present wo rk we established the precipitation conditions of Bi, Sr, Ca, Cu indiv idual oxalates and of the quaternary! mixture. The initial and thermal ly treated oxalate powders were characterized bq! XRD, IR, BET methods and TEM observation. The decomposition conditions were established ba sed on a DTA/TG study. The powders resulted from the decomposition of Bi and Cu oxalates contain the corresponding oxides and the Ca and Sr oxalates decomposition lead to the carbonates obtaining. In each case a high reactivity and a very small powder particle size were observed. A very good powder homogeneity has also been noticed in the final mix ture of oxalates. Compared to superconducting ceramic materials realiz ed by a classic route, the reactive oxalate powders allow the decrease of both thermal treatment periods and temperature, emphasizing a high microstructure homogeneity of the ceramic body. (C) 1998 Elsevier Sci ence Limited. All rights reserved.