Effects of Grinding and Uniaxial Press-forming on Sintered Superconductor in the Bi-Pb-Sr-Ca-Cu-O System

The formation behavior of an amorphous phase in grinding and its recrystallization behavior by heat-treatment of seed-added powder were observed using a starting powder of the high Tc phase (2223 phase) superconductor having the composition Bi_1.8Pb_0.4Sr_2.0Ca_2.0Cu_3.2O_y. The effects of uniaxial press-forming in the opposed anvil type high pressure apparatus were investigated in relation to the properties of sintered compacts (bulk density, phase microstructure, critical temperature, etc.). Grinding the starting powder in agate mortar for 10–20 min initiated the formation of an amorphous phase and nearly completely amorphous phase was obtained by grinding for 100min. The heat treatment (at 850°C for 2h) of the amorphous powder which was added by 50 wt% starting powder as seeds, resulted in the recrystallization to high Tc phase (2223 phase) in the presence of a trace of low Tc phase (2212 phase) Starting powder packed in a copper ring gasket was press-formed under high pressure (0.5–1.5 G Pa). A small amount of low Tc phase coexisted with high Tc phase in the specimen formed at 1.0 G Pa. The bulk density of the sintered compact prepared by the subsequent sintering at 850°C for 40h under one atmospheric pressure was 5.4g/cm³, and the critical onset and offset temperatures were 115K and 103K, respectively.