A family of glass/ceramic composite materials has been investigated for use as sealants in planar solid oxide fuel cells. These materials are modified versions of a barium calcium aluminosilicate glass developed previously for the same purpose. The composition of the glass in mole percentages is 35BaO + 15CaO + 5Al2O3 + 10B2O3 + 35SiO2. The glass seal was found to be susceptible to cracking during thermal cycling of the fuel cells.
The goal in formulating the glass/ ceramic composite materials was to (1) retain the physical and chemical advantages that led to the prior selection of the barium calcium aluminosilicate glass as the sealant while (2) increasing strength and fracture toughness so as to reduce the tendency toward cracking. Each of the composite formulations consists of the glass plus either of two ceramic reinforcements in a proportion between 0 and 30 mole percent. One of the ceramic reinforcements consists of alumina platelets; the other one consists of particles of yttria-stabilized zirconia wherein the yttria content is 3 mole percent (3YSZ).
In preparation for experiments, panels of the glass/ceramic composites were hot-pressed and machined into test bars. Properties of the test bars, including four point flexure strength, fracture toughness, modulus of elasticity, and density were determined. Four-point flexure strength and fracture toughness were found to increase with alumina or 3YSZ content (see figure). For the same mole percentage of ceramic, the increases in strength and fracture toughness were greater in the composites containing alumina than in the composites containing 3YSZ.
This work was done by Narottam P. Bansal of Glenn Research Center and Sung R. Choi of the University of Toledo. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.
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