Characterization of the thermal conductivity and mechanical properties of sheath alloy materials for Bi-2223 superconductor tapes

We evaluated the effects of adding alloying-element to the Ag sheath on the thermal conductivity and mechanical properties of Bi-2223 tapes. The therm al conductivity of Ag and Ag-alloys was evaluated by using the thermal inte gral method in the temperature range of 10 to 100 K, and correlated to the indirectly-measured values obtained from the density, specific heat, and th ermal diffusivity. It was observed that the additions of Au, Pd, and Mg to the Ag sheath significantly decreased thermal conductivity at low temperatu res, probably due to the presence of alloying-elements. Specifically, the t hermal conductivity of the Ag0.92Pd0.06Mg0.02 and Ag0.973Au0.025Mg0.002 all oys at 30 K was 28.9 and 59.2 (W/(m.K)), respectively, which is about 17 to 35 times lower than that of Ag (997.2 (W/m.K))). At the same time, these a dditions to the Ag sheath improved its mechanical strength It is believed t hat this improvement is related to the presence of dispersed alloying-eleme nts which leads to a smaller grain size.