Chapter 33. Sintering of Alumina Coating on Tungsten and Tungsten-Rhenium Alloy Wires

  1. John B. Wachtman Jr.
  1. Hardial S. Dewan1 and
  2. Amarjit Singh2

Published Online: 28 MAR 2008

DOI: 10.1002/9780470314050.ch33

A Collection of Papers Presented at the 94th Annual Meeting and the 1992 Fall Meeting of the Materials & Equipment/Whitewares Manufacturing: Ceramic Engineering and Science Proceedings, Volume 14, Issue 1/2

A Collection of Papers Presented at the 94th Annual Meeting and the 1992 Fall Meeting of the Materials & Equipment/Whitewares Manufacturing: Ceramic Engineering and Science Proceedings, Volume 14, Issue 1/2

How to Cite

Dewan, H. S. and Singh, A. (1993) Sintering of Alumina Coating on Tungsten and Tungsten-Rhenium Alloy Wires, in A Collection of Papers Presented at the 94th Annual Meeting and the 1992 Fall Meeting of the Materials & Equipment/Whitewares Manufacturing: Ceramic Engineering and Science Proceedings, Volume 14, Issue 1/2 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470314050.ch33

Author Information

  1. 1

    Materials Research Laboratory Pennsylvania State University University Park, PA 16802

  2. 2

    Laboratory for Plasma Research University of Maryland College Park, MD 20742

Publication History

  1. Published Online: 28 MAR 2008
  2. Published Print: 1 JAN 1993

ISBN Information

Print ISBN: 9780470375235

Online ISBN: 9780470314050

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Keywords:

  • tungsten rhenium alloy wires;
  • oxidation avoidance;
  • radio frequency system;
  • thermal conductor;
  • alumina coating

Summary

A thin (≈0.003 in.) electrically insulating coating is required on tungsten and tungsten-rhenium alloy wires for use as heating elements inside thermionic cathodes. Since the cathodes operate at 800P-110CPC and a very high vacuum has to be maintained in the sealed-off electron tubes, the choice of material falls on high-purity alumina, which has a low vapor pressure at high temperatures. The requirements of a sintering temperature of ≈ 165(PC, high purity, small grain size, flexibility, good adhesion to the wire, oxidation avoidance, and carbonization present many problems. The paper describes a process and equipment that use the high energy-coupling efficiency of radio frequency induction heating. A special crucible of molybdenum holds the coated heater element and humidified hydrogen provides the reducing atmosphere. The sintering of Al2O3 coating is achieved in about 3 min with a 5 kW radio frequency system.