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Thermo-mechanical Behavior of Glass Based Seals for Solid Oxide Fuel Cells

Singh, Sandeep
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379341

Abstract Details

2010, PhD, University of Cincinnati, Engineering and Applied Science: Materials Science.
Availability of durable seals for planar solid oxide fuel cells (pSOFC) is one of the main limitations to the fabrication of reliable fuel cell stacks. Glass and glass ceramics are often used as sealing materials to seal cell components, because of their flexibility in matching coefficient of thermal expansion with sealing components. In this work glass and glass composites containing ceramic fillers with suitable thermal, chemical and sealing behaviors are explored for use in a novel concept on self-repairable seals. This concept requires a glass with low viscosity at the SOFC operating temperature, which contradicts with the requirement of creep resistance. A silicate glass with self-healing capability is selected based on their thermo-mechanical properties as the starting material for seals, but this glass may suffer from excessive flow at elevated temperatures, which leads to squeezing of the glass. Therefore, to alleviate this glass composite with fillers and suitable thermo-mechanical properties are promising because the glass matrix can flow to mitigate stresses and heal cracks, whereas the filler controls the flow behavior of the glass and improves the creep resistance and seal strength. In order to make glass composites, a range of ceramic fillers such as Al2O3, MgO, and YSZ are considered. The effect of filler materials and filler volume fraction on the thermo-mechanical properties such as coefficients of thermal expansion, glass softening temperature and viscosity are investigated. Sessile drop method is used to investigate the glass and glass composite properties useful for sealing. The variation of contact angles with temperature and time are measured from which activation energy for wetting, work of spreading, viscosity and surface tension are obtained. The surface tension values are determined based on sessile drop model by following Dorsey and Porter approaches. A new approach based on sessile drop model and using wetting dynamics is investigated to determine viscosity at elevated temperatures. The viscosity values are also obtained using a number of different approaches such as sessile drop method, creep measurement, Vogel-Fulcher-Tamman (VFT) and Moynihan model equations. The experimentally measured viscosity values are fitted with modified-VFT model equation to construct viscosity-temperature curve over a wide range. Long term thermal, chemical, electrical resistivity and volatilization stabilities of sealing glass are evaluated in dual oxidizing and wet reducing environments at 8000 C. The chemical compatibility of a self healing glass with cell components shows no microstructural evidence of any new reaction phases present at the interface. The measured electrical resistivity of glass at is and is stable over the test period of 1000 h. The weight loss stability test showed negligible weight loss (1 wt. % for the time period of 5 years). Based on these results, the selected glass and glass composites with YSZ filler seem to be a promising candidate for SOFC seals.
Raj Singh, ScD (Committee Chair)
Rodney Roseman, PhD (Committee Member)
Relva Buchanan, ScD (Committee Member)
Vesselin Shanov, PhD (Committee Member)
140 p.
Materials Science
Glass Seals; Glass Composites; Sessile Drop; Surface Tension; Viscosity; Creep

Recommended Citations

Citations

  • Singh, S. (2010). Thermo-mechanical Behavior of Glass Based Seals for Solid Oxide Fuel Cells [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379341

    APA Style (7th edition)

  • Singh, Sandeep. Thermo-mechanical Behavior of Glass Based Seals for Solid Oxide Fuel Cells. 2010. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379341.

    MLA Style (8th edition)

  • Singh, Sandeep. "Thermo-mechanical Behavior of Glass Based Seals for Solid Oxide Fuel Cells." Doctoral dissertation, University of Cincinnati, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1288379341

    Chicago Manual of Style (17th edition)

ucin1288379341
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© 2010, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.