Promotion of melt-assisted growth in Bi-2223 tapes utilizing rapid heating rates

Abstract

Recent differential thermal analysis studies on green Bi-2223 tapes showed two phase transitions, with onset temperatures 800 and 820 °C. From microstructural examination of the long-term phase formation in the tapes the higher temperature endotherm was associated with a partial melt. In this study it is demonstrated how control of the heating rate can promote the partial melt (characterized by DTA), and thereby improve the transport current, Ic. XRD, SEM and transport measurements in field show microstructure features typical of an increased volume of liquid phase: a reduction in secondary phase volume and pores with a corresponding increase in c-plane texture.

The affect of transients on secondary phase formation in multifilamentary (Bi, Pb)2223/Ag composite tape

“…Higher temperatures form more liquid, so rearrangement and densification can occur but secondary phase formation can result. The ability to control the melt to some degree as regards better superconductor transport properties is shown in a separate publication [7].…”

“…Previous work in this study has demonstrated a reduction in secondary phases which is thought to be due to an enhancement of the volume of liquid phase [6,7]. The focus of this work is on making a link between the transients in the initial stages of reaction and the secondary phase formation after prolonged heat treatment.…”