Improving Jc Reproducibility in Ag-Sheathed Bi-Based Tapes by a Non-Linear Temperature-Time Sintering Process
An improvement in reproducibility of the critical current density(Jc) has been obtained in Ag-sheathed Bi2223 tapes made by the powder-in-tube method using a non-linear temperature-time sintering process. In this process, the sintering temperature was slowly raised from the temperature of emergence of a liquid phase (about 800°C) to the temperature of sufficient crystal growth of 2223 phase (830°C), so that the rate of liquid formation could be controlled and rapid growth of the non-superconducting phases could be prevented. A reduction of about 30 % per pass during rolling, one intermediate pressing and total sintering time less than 120 hours were employed in this process. The texture of the tape made by this process is better than that of the tape made by isothermal sintering. An average Jc of 3.18×l04 A/cm2 at 77 K in self-field with a deviation 17 % was measured in tapes made by this method, compared with an average Jc of 2.09×104 A/cm2 at 77 K with a deviation up to 80 % in tapes made by a normal isothermal sintering. Doping pure silver powder into incompletely reacted powder is used to control transformation from 2212 to 2223 and enhance the texture. The Jc-field dependence was improved by increasing number of pressing. The fine dispersed phase of Ca-Sr-Pb-0 was observed by EDX analysis in tapes made by the non-linear sintering, while the Sr-Ca-Cu-O phase in tapes made by isothermal sintering was commonly found.
KeywordsSinter Process Critical Current Density Silver Powder Isothermal Sinter Sinter Procedure
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