DENSIFICATION BEHAVIOR DURING HOT-PRESSING OF BI-PB-SR-CA-CU-O SUPERCONDUCTORS

Bi1.84Pb0.34Sr2.03Ca1.9Cu3.06Oy bulk superconductors with various rela tive densities were prepared by hot pressing in the temperature range 780 degrees C-840 degrees C and the pressure range of 4.9 MPa-24.5 MPa in air for 2 h. The relationship between porosity, p, and hot pressin g conditions was formulated using the following equation: In(p) = -alp ha(o) exp(-E/RT)P + In(p(o)), where P was the hot-pressing pressure, p (o) the porosity of the compact body, E an apparent activation energy for densification, T the temperature, R the gas constant, and alpha(o) a constant. The apparent activation energies were 184 KJ/mol and 526 KJ/mol in the lower- and higher-temperature ranges in comparison to 82 0 degrees C, respectively. The densification mechanisms in the lower a nd higher temperature ranges are discussed in terms of plastic flow, p article rearrangement and the formation of liquid phase.