Microstructure of Bi-superconducting Ceramics Prepared by Hot-extrusion Processing

Abstract

Bi₂Sr₂CaCu₂O_x ceramic powder prepared by a solid state reaction was encapsulated in Ag can with a dimensions of 32^φ(O.D.)-20^φ(I.D.)×55 ?? mm. The bullet (can containing ceramic powder) was
preheated at 840°C for about 10 min and was extruded rapidly to avoid excessive heat loss.
Many kinds of disordered structure were observed in the hot-extruded ceramics by TEM. They were mechanically disordered grain boundaries, microfractured grains, and amorphous regions. The disordered structure regions changed, however, to polycrystals composed of small grains without grain boundary second phase after annealing at 800°C for 1 hr. The densification mechanism of the Bi-superconducting ceramic powder during the hot-extrusion processing was discussed by considering the microstructural change.