EFFECT OF LEAD LOSS AND SHEATH STRUCTURE ON PHASE-FORMATION AND ALIGNMENT IN (BI,PB)(2)SR2CA2CU3O10+DELTA/AG COMPOSITE CONDUCTORS

The effects of metallic constituent evaporation and sheath structure on grain growth and alignment in silver-sheathed (Bi,Pb)(2)Sr2Ca2Cu3O10+delta (Bi-2223)/Ag composites have been investigated by inductively coupled plasma/atomic emission spectroscopy (ICP/AES), X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy, Specimens of Bi-2223/Ag composites fabricated by the oxide-powder-in-tube technique mere peeled (opened) lengthwise to expose the ceramic powder core, and then heat-treated in 0.075 atm of oxygen for selected temperatures and times, The results were compared with those for as-processed samples with closed silver sheaths treated under identical conditions, ICP/AES analysis indicated that lead was the only metallic element to undergo substantial evaporation during annealing of opened samples, The lead-release process in parallel with the Bi-2223 formation reaction had an activation energy of similar to 25 kJ/mol, Lead loss from the opened samples resulted in incomplete conversion to Bi-2223, The combined results show that the silver sheath effectively prevents evaporative lead loss, preserves and promotes densification, and induces texturing of the layered phases.