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  News in Brief

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  Wow! Fermilab Confirms the Tau

  Superweld

  Working Science

  People

  About

  Subscribe Free

















This issue...

  News in Brief

  View from the Inside

  Wow! Fermilab Confirms the Tau

  Superweld

  Working Science

  People

  About

  Subscribe Free

Superweld

Unlocking the Potential of High-Temperature Superconductors

by Ralph Batie

"High-temperature" copper oxide superconductors were discovered over ten years ago. These materials, with the ability to remain superconducting at liquid-nitrogen temperatures and above, were hailed as the means to exciting new applications in electric power. This promise still has not been realized because there has been no reliable way to join the materials into larger structures and shapes without sacrificing its ability to carry high critical current, until now…


Researchers at Argonne National Laboratory have recently succeeded in welding small high-temperature superconductors into larger components and components of different shapes without increasing the material's electrical resistance.

The commercial potential for superconductors has been blocked by the size and shape limitations of superconductor materials. The largest samples of superconductor materials currently produced are only one or two inches in diameter. Until now, researchers have found it difficult to join those small sections into superconductors that are large enough to be commercially useful without interfering with the electrical flow.

"This innovation is the key to widespread use of high-temperature superconductors in the electric power industry," said Boyd Veal, who developed the technique along with Helmut Claus, Hong Zheng, Paul Paulikas, Lihua Chen, and George Crabtree.

Some small commercial applications of high-temperature superconductors are currently in use, but applications like current leads, fault current limiters, high-energy-density motors, and energy storage devices require much larger or longer superconducting structures than currently exist.

Veal explained that to join superconductor materials into larger components, the entire structure must have essentially the same crystal orientation (a "single domain" or "texture") if the material's superconducting properties are to be retained.

Argonne's superconducting weld technique
This illustration shows how well the superconductor welding technique works on a ring of superconducting material. The left panel shows the magnetic field produced by a superconducting current circulating around the unbroken 12-mm diameter ring. In the center panel, the ring is cut, and the magnetic field drops as the electric current ceases to flow. In the right panel, the ring has been "welded" back together with the new process, and the magnetic field produced is within 95% of the field for the unbroken ring.

The new welding technique bonds pieces of a high-temperature superconducting material called yttrium-barium-copper-oxide (YBCO) together by sandwiching thin layers of a similar compound called thulium-barium-copper-oxide (TmBCO) between the pieces. TmBCO melts at a temperature about 20°C lower than YBCO so that when the materials are heated to a temperature midway between their melting points, the TmBCO liquifies while the YBCO remains solid. The YBCO crystal structure provides a template for the liquefied TmBCO to follow as it cools and recrystallizes. As the joint solidifies, the atoms of the TmBCO filler align with the YBCO crystal structure to form a single, continuous connection across the weld joint. This results in a weld that preserves the YBCO crystal structure, maintains its mechanical strength, and most importantly, continues to carry the electrical current.

The Argonne team is continuing its research to improve the technique for an even more reliable weld, recently testing a new composition of the filler, a mixture of YBCO and silver, which melts at a temperature 30°C lower than YBCO.

This research was developed under a cooperative research and development agreement with Superconductive Components, Inc. (SCI), Columbus, Ohio, and funding from the U.S. Department of Energy's Office of Science, Laboratory Technology Research Program and Office of Basic Energy Sciences, and by the National Science Foundation, Science and Technology Center for Superconductivity.

Contact: Boyd Veal, Argonne National Laboratory, veal@anl.gov


Related Information:

Superconductor Information for the Beginner, Superconductors.Org

"New Technique Does Super(conducting) Weld", Argonne National Laboratory, press release.

Superconductivity Research Leads to Improved Applications, Argonne National Laboratory

High Temperature Superconductors, Oak Ridge National Laboratory

Materials By Design: Superconductors, Cornell University

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To join superconductor materials into larger functioning components, the entire structure must have essentially the same crystal orientation.
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