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Preoxidation Study of Fe-Ni-Co (KOVAR) Alloy on Glass to Metal Sealing Performance

Toloue Farrokh, Najibe | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43653 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Askari, Masoud; Kaflou, Ali
  7. Abstract:
  8. The Fe-Ni-Co alloy to borosilicate glass seals have been used for many years as hermetic and electrically insulating seals. It is not only excellent in thermal expansion matching but also in good wettability and bond strength too. Oxidation of Kovar was performed in Water vapor, Saturated Nitrogen and N2-H2-H2O atmosphere in tube furnace. Oxide layer composition and thickness changed by varying in oxidation temperature and time. XRD analysis showed different Iron oxides in oxide layer, FeO, Fe3O4 and Fe2O3. However in the third atmosphere no Hematite observed. Increasing oxidation temperature and time result in increasing sample weight gains and roughness. Oxide layer microstructure also was investigated by optical microscopy and scanning electron microscopy. We could have intergranular oxides inn higher oxidation temperatures and time.Sessile drop method was used for investigating wettability of molten glass on Kovar samples which were oxidized differently in N2-H2-H2O atmosphere. In this test either tube furnace or induction heating system was used. Contact angle and molten drop shape showed an improvement in wettability by increasing oxides containing Fe+2. Finally glass to kovar seal were performed in both tube furnace and induction heating systems. The phase which observed in joint interface in induction heating system was finer than interfacial phase formed in tube furnace. Also oxide layer in induction heating joining process was not dissolved in glass completely.
  9. Keywords:
  10. Thermodynamics ; Wetting ; INDUCTION HEATING ; Kovar Alloy ; Glass to Metal Sealing ; Oxidation in Controlled Atmosphere ; Radiation Heating

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