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Coiling a ceramic superconductor.

Coiling a ceramic superconductor

Stretched end to end, the superconducting wire in the coil shown below spans 30 feet. Though it can carry only a tenth of the current needed for building practical electrical motors, it represents a step toward such devices, says ceramics engineer Stephen E. Dorris, who helped develop the wire at Argonne (Ill.) National Laboratory. Reaching lengths of up to 50 feet, the Argonne wires may be the longest superconducting strands around, he asserts. Already, Reliance Electric Co. in Cleveland has used one of these coils in a small, experimental motor, with which the company hopes to study technical challenges to building larger superconducting motors for use by the electric utility industry.

"Efficiency losses in a superconducting motor are less than half those in a conventional motor," notes research manager James S. Edmonds of the Electric Power Research Institute in Palo Alto, Calif., which funds the work.

Unlike coils made with copper and other normally conductive metals, which pose varying degrees of energy-sapping resistance to electrical current, the superconducting coils can carry current with no resistance whatsover so long as they are held at liquid nitrogen temperatures (77 kelvins). The Argonne researchers made their coil out of the superconducting ceramic yttrium-barium-copper-oxide, also known as "1-2-3." The process involves mixing 1-2-3 powder with some acrylic resin and strength-giving silver and extruding the malleable mixture into a wire, which then gets a coating of "2-1-1" power -- 2 parts yttrium and 1 each of barium and the oxide. The scientists wind the preparation into a coil and then heat it. The heat treatment burns off the acrylic while sintering the 1-2-3 powder into a continuous coil and the 2-1-1 into a green-colored insulating coat.

"We used the 2-1-1 modification as an insulator because other materials interferred with the chemical properties of the superconducting wire when the coil was fired in a furnace," explains Argonne's Roger Poeppel.
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Author:Amato, Ivan
Publication:Science News
Date:Jun 2, 1990
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