MICROSTRUCTURE OF MELT-PROCESSED BI2SR2CACU2OY AND REACTION-MECHANISMS DURING POST HEAT-TREATMENT

Phase compositions and microstructures of melt processed 2212 were studied. 2212 starting powder was cooled from temperatures between 910-degrees-C and 1100-degrees-C in air at rates ranging from 350 K/min to 0.083 K/min. The solidification sequence was established for all cooling rates. Under all conditions the Bi-free (Sr, Ca)CuO2 (01x1) is the primary phase. The one-layer solid solution 11905 nucleates on this phase. The residual liquid solidifies to a glassy state, decomposes into the eutectic of Cu2O and Bi2Sr2.1Ca0.9Ox, or reacts with the primary phase and the 11905 forming 2212 at high, intermediate, or low cooling rates, respectively. Post solidification heat treatment at 850-degrees-C in air leads to partial remelting. The Cu-rich liquid reacts with 11905 and 01x1 forming 2212. Subsequent solid/solid reactions lead to a high volume fraction of 2212 with almost ideal 2:2:1:2 stoichiometry.