PHASE REGIONS AND KINETICS OF FORMATION OF (BI,PB)(2)SR2CA2CU3OX IN AG-SHEATHED TAPE

Ag-sheathed (Bi,Pb)(2)Sr2Ca2Cu3Ox (2223) tapes were made by the oxide- powder-in-tube method. Tapes were heat treated isothermally at several different temperatures in 7.5% O-2/Ar, then quenched into oil to reta in the phase assemblages at the reaction temperatures. 2223 formed bet ween similar to 810 degrees and similar to 837 degrees C. The Avrami e quation was applied to describe the kinetics of 2223 formation from a mixture of Bi2Sr2CaCu2Ox and nonsuperconducting phases, mainly Ca2PbO4 and CuO. The calculated Avrami exponent, n approximate to 1, indicate d that the kinetics in this system could be described as a diffusion-c ontrolled, two-dimensional nucleation and growth process. The apparent activation energy for forming 2223 was similar to 2900 kJ/mol from si milar to 817 degrees to similar to 825 degrees C and similar to 890 kJ /mol from similar to 825 degrees to similar to 837 degrees C. A temper ature-time-transformation diagram was constructed based on the kinetic data; it describes the transformational behavior of this particular s ystem.