Bi(Pb)-Sr-Ca-Cu-O系超伝導体の緻密化と臨界電流密度に及ぼす再加圧成形の効果

概要

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A starting powder for sintering of superconductors in the Bi(Pb)-Sr-Ca-Cu-0 system was prepared by calcining the mixture of a high Tc phase (Bi1.8Pb0.4Sr2.0Ca2.0Cu3.2Oy) and 0.4 mol CaC03 at 800°C for 2h. The sintered compacts were obtained by the two-step sintering. where the starting powder which was press formed at 1-5t/cm2, was primarily sintered at 850t for 20h, then re-press formed at 2-5t/cm2 and finally sintered at 8501; for 120h. The effects of the re-press forming on the densification behavior and superconducting properties were investigated by employing the above two-step sintering. The bulk density of the compact which was primarily sintered after press forming at 3t/cm2 was 4.2g/cm3, while the density increased up to 5.2g/cm3 by secondary sintering after re-press forming at 5t/cm2. A linear relation was found between the Jc values and the bulk densities of the compacts, which were prepared by one-step sintering or two-step sintering at 8500 for 120h. The Jc(77K) value of the compact of theoretical density was estimated by extrapolation to attain a magnitude of 104A/em2.
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