DEFORMATION OF SILVER-SHEATHED OXIDE SUPERCONDUCTING TAPES BY TRAPPEDGASES

A simple model was developed to describe the deformation in long silve r-sheathed oxide superconducting tapes caused by the thermal expansion of air trapped within the conductor and by carbon dioxide released by the decomposition of SrCO3 in the precursor powder during heat treatm ent. The analysis presented can be extended to include other carbon-co ntaining compounds, impurities and gases released during the annealing process. The model assumes a zero-strain deformation process of the t hin silver sheath in response to the gas pressure developed within the conductor due to heating. Results show that swelling (uniform deforma tion along the conductor length) increases linearly with temperature. For a carbon-free tape, swelling increases with decreasing precursor p owder packing density. The reverse is true for tapes that contain carb on which is distributed uniformly within the tape. A carbon content of approximate to 0.001% by weight produces swelling similar to that pro duced by air. Increasing carbon content increases swelling. Carbon con tent in excess of 0.5% by weight will deform the con ductor to the ext ent that elastic/plastic deformation can occur. Discrete SrCO3 particl es dispersed among the precursor powder produce bubbles (localized def ormation). The size and concentration of these bubbles depend on the S rCO3 particle size and concentration. For a given carbon content, smal l SrCO3 particles form a large number of bubbles, which merge together resulting in swelling along the conductor length. Large SrCO3 particl es, on the other hand, form only a few discrete bubbles whose size inc reases with particle size.