EFFECTS OF OXYGEN-PRESSURE ON PHASE EVOLUTION AND MICROSTRUCTURAL DEVELOPMENT IN SILVER-CLAD (BI, PB)2SR2CA2CU3O10+DELTA COMPOSITE CONDUCTORS

The kinetics of phase evolution and the development of microstructure in silver-clad composite conductors containing a Bi-Pb-Sr-Ca-Cu-O powder with a nominal stoichiometry of Bi1.7Pb0.4Sr2Ca2-Cu3O10+delta were studied as a function of oxygen partial pressure (pO2), temperature, powder stoichiometry, and powder pre-treatment. The optimum temperature for growth kinetics of the Bi-2223 phase increased as the oxygen partial pressure was increased from 0.02 to 0.21 atm. The width of the phase stability region was largest for pO2 = 0.075 atm and smallest for pO2 = 0.21 atm. It was found that for a 25-h heat treatment, the reaction kinetics were the fastest in 0.075 atm of oxygen at temperatures between 825-degrees and 830-degrees-C. The secondary phase particles (observed by scanning electron microscopy) were smaller for lower pO2 (0.02 and 0.075 atm) than for higher pO2 (0.13 and 0.21 atm).