Metallo-Organics Derived Tractable Resins for Ybco Superconducting Fiber Fabrication
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METALLO-ORGANICS DERIVED TRACTABLE RESINS FOR YBCO SUPERCONDUCTING FIBER FABRICATION K.C. Chen, A. Y. Chen and K. S. Mazdiyasni General Atomics, PO Box 85608, San Diego, CA 92138-5608 ABSTRACT Soluble resins were prepared by controlled hydrolysis of yttrium isopropoxide, barium isopropoxide and copper ethylhexanoate. The resins were converted to cohesive, viscous, fluid and precipitated states by the addition of different combinations of binary polar and non-polar organic solvents. Viscosity and spinnability of the resins were critically dependent on the solvent constituents. Continuous pre-ceramic fibers were spun from these resins and single phase YBa2Cu3Oy superconducting fibers with Tc=91.5K and AT=1.5K have been obtained. INTRODUCTION The magnetic applications of a superconducting cable require high critical currents, strengths and modulus of the superconducting fibers. To meet these requirements, the fiber must have the following features: chemical stoichiometry, phase purity, high density, crystallographic orientation in the c direction, uniform fine microstructure and clean grain boundaries. There are few known methods for fabricating superconducting fibers of 20-100 g±m in diameter without an outer cladding or center wire as support. These methods include metalalloy, powder-in-binder [1], powder in sol [2], sol-gel and metallo-organics [3-7]. In order to spin fibers directly from the metallo-organic derived resins, the resin not only has to meet the requirements for the final ceramic fiber, but must also have high viscosity, viscoelasticity, cohesiveness, green strength, low shrinkage and high oxide content. In this paper, we discuss the preparation of metallo-organic derived tractable resins that possess several key parameters of the aforementioned properties for continuous spinning of single phase YBa 2Cu 3Oy fibers. EXPERIMENTAL PROCEDURE Yttrium isopropoxide/isopropanol solutions, barium isopropoxide/isopropanol solution and copper ethylhexanote/isopropanol stock solutions were prepared as described previously [8]. Solutions containing stoichiometric (YBa 2Cu 3Oy) amounts of required elements were prepared by pipetting the calculated volume from each stock solution into a 500 ml three-neck round bottom flask. First, barium isopropoxide and yttrium isopropoxide were mixed, and a clear yellowish solution was obtained. A green precipitate formed when copper ethylhexanoate solution was later introduced. This solution was refluxed gently in a dry nitrogen atmosphere for 2 hours. This precipitated solution was then hydrolyzed by adding a mixture of water/isopropanol, using 10 equivalents of water per mole of yttrium isopropoxide while the solution temperature was kept at 50-60°C. The greenish precipitate dissolved after adding water and a clear dark green solution formed. This solution was concentrated and initially dried in a rotary evaporator, was further dried in a vacuum oven and was then ground into powder for storage. Suitable viscosity could be achieved when the dried powder was dissolved with the pro
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