Experimental observations of thermal spikes in microwave processing of ceramic oxide fibers

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Microwave heating of alumina/silica fiber tows in a single-mode microwave cavity at 2.45 GHz have produced a surprising thermal spike behavior on the fiber bundles. During a thermal spike, a ``hot spot`` on the tow brightens rapidly, persists for a few seconds, and rapidly extinguishs. A hot spot can encompass the entire tow in the cavity or just a localized portion of the tow. Some local hot spots propagate along the fiber. Thermal spikes are triggered by relatively small (<15%) increases in power, thus having obvious implications for the development of practical microwave fiber processing systems. A tow can be ... continued below

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7 p.

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Vogt, G. J.; Unruh, W. P. & Thomas, J. R. Jr. April 1, 1994.

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Description

Microwave heating of alumina/silica fiber tows in a single-mode microwave cavity at 2.45 GHz have produced a surprising thermal spike behavior on the fiber bundles. During a thermal spike, a ``hot spot`` on the tow brightens rapidly, persists for a few seconds, and rapidly extinguishs. A hot spot can encompass the entire tow in the cavity or just a localized portion of the tow. Some local hot spots propagate along the fiber. Thermal spikes are triggered by relatively small (<15%) increases in power, thus having obvious implications for the development of practical microwave fiber processing systems. A tow can be heated through several successive thermal spikes, after which the tow is left substantially cooler than it was originally, although the applied microwave electric field is much larger. X-ray diffraction studies show that after each temperature spike there is a partial phase transformation of the tow material into mullite. After several excursions the tow has been largely transformed to the new, less lossy phase and is more difficult to heat. Heating experiments with Nextel 550 tows are examined for a pausible explanation of this microwave heating behavior.

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7 p.

Notes

OSTI as DE94009348; Paper copy available at OSTI: phone, 865-576-8401, or email, reports@adonis.osti.gov

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  • Spring meeting of the Materials Research Society (MRS),San Francisco, CA (United States),4-8 Apr 1994

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  • Other: DE94009348
  • Report No.: LA-UR--94-986
  • Report No.: CONF-940411--5
  • Grant Number: W-7405-ENG-36
  • Office of Scientific & Technical Information Report Number: 10139297
  • Archival Resource Key: ark:/67531/metadc1316946

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  • April 1, 1994

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  • Nov. 3, 2018, 11:47 a.m.

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  • Nov. 13, 2018, 1:18 p.m.

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Vogt, G. J.; Unruh, W. P. & Thomas, J. R. Jr. Experimental observations of thermal spikes in microwave processing of ceramic oxide fibers, article, April 1, 1994; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1316946/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.