Effect of the phase assemblage of the precursor powder on the phase transformation and microstructure of Ag/Bi-2223 tapes

The effect of the phase assemblage of the precursor powder on the properties of Ag/Bi-2223 tapes was investigated. The phase assemblage of the precursor powder was controlled by changing the calcination temperatures from 800 to 855 degrees C or by adding 2223 seed particles to the precursor powder. The phase transformation kinetics, microstructure and transport properties of tapes were strongly dependent on the phase composition of precursor powder. The tapes fabricated from the powder calcined at lower temperatures (800 and 820 degrees C), which contained no 2223 phase and a relatively large amount of secondary phase, resulted in a microstructure with a larger grain size and a higher transport critical current. These tapes also appeared to have an appreciable incubation period in an isothermal annealing experiment with various soaking times. The phase transformation kinetics and microstructural development was pertinent to the nucleation and growth process for the mechanism of 2223 formation.