Rapid Thermal Processing Of High Temperature Superconducting Fiber
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RAPID THERMAL PROCESSING OF HIGH TEMPERATURE SUPERCONDUCTING FIBER J.W. HALLORAN*, M.J. NEAL*, D.S.GINLEY**, E.L. VENTURINI** ,J.F. KWAK* BAUGHMAN **M.A. MITCHELL** ,B.MOROSIN **,S.N. BASU ***nd T.E. MITCHELL*** *CPS Superconductor Corporation, Laboratories, Albuquerque, NM 87185 Alamos, NM 87545
R.J.
Milford, MA 01757 **Sandia National ***Los Alamos National Laboratories, Los
Abstract We report on the rapid thermal processing (RTP) of YBa 2 Cu 3 O7 (Y-123) fibers. Unsintered fibers are densified by RTP. We show that fibers which were originally semiconducting and tetragonal before RTP form normal twinned orthorhombic material after processing for 2-4 seconds above 1000°C with a 3 min. cool down in oxygen. They subsequently show Tc to 90K and magnetization indicative of substantially shielding. We present the effects of varying the RTP parameters on the morphology, phase, and superconducting properties of a number of tetragonal and orthorhombic Y-123 fibers. Introduction We have previously reported that Rapid Thermal Processing (RTP), using heat treatments as short as one second at temperatures around IO00°C, is an effective processing technique for high temperature superconductors [1,2]. RTP of YBa 2 Cu 3 O7 (Y-123) fibers has produced material with Tc,r-CPf up to 90K and self field Jc 2 to 1200 A/cm . RTP rapidly densifies unsintered material, creating a microstructure characteristic of the fiber composition, RTP temperature and time. Of particular interest is the fact that RTP annealed Y-123 is superconducting immediately after the RTP anneal, without requiring the 500°C oxygen anneal which is conventional for Y-123. Indeed, conventionally sintered Y-123 fibers, which are semiconducting in their as-sintered state, become superconducting after an RTP treatment, indicating that very rapid oxygenation occurs during RTP. In this paper we discuss the development of the microstructure when sintering occurs by RTP and characterize the phenomenon of rapid oxygenation by examining superconducting properties of pre-sintered Y-123 after RTP treatment. EXPERIMENTAL PROCEDURE Fabrication of Fibers
Fibers were produced using a proprietary process in which Y-123 powders are compounded with a thermoplastic resin so they can be spun into continuous "green" fibers using a conventional textile fiber spinning machine. Most fibers used in this study had a green diameter of 125 microns. The powder was a phase pure Y-123 with 1.6 micron average particle diameter. Copper oxide-rich fibers were prepared with a 5 wt% admixture of CuO. Fibers which were RTP annealed in the unfired state had undergone a binder burnout in which the fibers were heated in air at 20°C/minute to 500°C, held for 10 minutes, then cooled to room temperature at 10°C/minute. This treatment removes most of the organic material, but does not allow any sintering of the Y-123. Pre-sintered fibers received a binder burnout and a 945°C/30 min sintering anneal in a continuous furnace, yielding a sintered density about 90% of theoretical. Rapid Thermal Processing Burned
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