FORMATION AND PREVENTION OF BUBBLES WHEN MELT PROCESSING AG-SHEATHED BI2SR2CACU2OX (2212) CONDUCTORS

We observed that the extent of bubbling of Ag-sheathed Bi2Sr2CaCu2Ox t ape varied with the partial pressure of oxygen (p(O2)) in the surround ing atmosphere during melt processing. Tape that did not bubble when p rocessed in air or 50% O2 was severely bubbled when processed in 100% O2 (P(total = 0.1 MPa). When a tape was held at the maximum melt proce ssing temperature (approximately 890-degrees-C) and the atmosphere was changed from air or 50% O2 to 100% O2, bubbles formed in the previous ly unbubbled tape. These bubbles often grew to be tens of centimetres in length and are called tunnels. The formation of tunnels is thought to be driven by the p(CO2) in the sheath from residual carbon in the p owder. Increasing p(O2) is thought to either increase p(CO2) or change the physical properties of the Ag allowing the sheath to deform in 10 0% O2.