Rapid consolidation of YBa2Cu3O7 powder
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Electrical current in a powder transits particle contact points, whose high resistance localizesI2R heating. The occurrence of sintering at particle contact points suggests an efficient means of consolidating the difficult-to-sinter ceramic superconductor YBa2Cu3O7.
A specially fabricated apparatus for simultaneous application of pressure and passage of electrical current accomplished the consolidation. Computerized control continuously adjusted current levels for changes in specimen resistance, maintaining a constant level of power dissipation. Power dissipation of 55 W for one minute produced solid specimens, either cylinders 3 mm in diameter x 4 mm, or blocks 2 mm x 5 mm x 5 mm. The specimens were annealed in flowing oxygen, save for one control.
Annealed specimens exhibited Meissner effect, transition to zero resistivity near 90 K, andjc ≈ 75 A/cm2. The scanning electron microscope (SEM) showed porous microstructures for all but one specimen. The control had a similar microstructure, showing annealing added little consolidation. This work demonstrates the rapid consolidation of YBa2Cu3O7 powder into a solid which upon oxygen annealing exhibits true superconductivity.
KeywordsPower Dissipation Critical Current Density Ohmic Heating Load Frame Material Shaping Technology
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