Controlled Over Pressure Processing of Bi2223 Long Length Wires

TLDR

Controlled overpressure densifies Bi2223 filaments, preventing liquid‑nitrogen penetration and eliminating ballooning from trapped nitrogen during temperature cycling. The process raises critical current by over 30 %, yields tensile strengths above 250 MPa at 77 K, heals cracks and porosities, and enables commercial power‑cable, magnet, and other applications.

Abstract

By applying the high isostatic pressure in the final heat treatment, we have raised the critical current (I/sub c/) of multifilamentary (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ (Bi2223) long length wires by greater than 30%. Mechanical performance has reached levels over 250 MPa critical tensile stress at 77 K. The density of filaments in Bi2223 wire was estimated from mass density measurement and found to be increased to filament density. The controlled overpressure process has been found to advantageously heal cracks and porosities of filaments. Densification of the filaments prevents liquid nitrogen penetration during long term exposure to liquid nitrogen of Bi2223 wire for use in power cable applications. Ballooning caused by trapped nitrogen, that expands when warming up to room temperature, doesn't occur in the controlled overpressure processed wire. These high performance levels in long length Bi2223 wires have enabled commercial level products and projects such as power cables, magnets and many others.