R. K. Brow, D. S. Reis, University of Missouri-Rolla, Rolla, MO
The material requirements for hermetic seals for solid oxide fuel cells (SOFC) are severe. For most SOFC designs, the sealing material must have thermal expansion characteristics that do not contribute to the formation of thermal stresses between a variety of ceramic and metallic materials used in the SOFC stack; must be thermochemically compatible with those other materials; must remain stable at elevated temperatures (700-800°C) over the lifetime of the SOFC (thousands of hours), in the oxidizing and reducing environments of an SOFC cell. In addition, the sealing conditions are limited by the thermal stability of other materials in the stack, leaving the materials designers with a relatively narrow processing window for making the seals. We will review the desirable properties for glasses designed for hermetic seals between Y-stabilized zirconia (YSZ) electrolytes and oxidation-resistant Cr-Fe interconnect alloys and will discuss the relationships between glass composition and structure that help determined the desirable properties. Highly depolymerized alkaline earth/zinc silicate structures have the viscosity characteristics necessary to form a seal at 800-850°C and then be crystallized to form thermo-chemically stable glass-ceramics with the requisite thermal expansion characteristics for these seals. Studies of the long-term interfacial reactions between the glass-ceramics and the interconnect alloys will be reviewed.
Summary: The material requirements for hermetic seals for solid oxide fuel cells (SOFC) are severe. For most SOFC designs, the sealing material must have thermal expansion characteristics that do not contribute to the formation of thermal stresses between a variety of ceramic and metallic materials used in the SOFC stack; must be thermochemically compatible with those other materials; must remain stable at elevated temperatures (700-800°C) over the lifetime of the SOFC (thousands of hours), in the oxidizing and reducing environments of an SOFC cell. In addition, the sealing conditions are limited by the thermal stability of other materials in the stack, leaving the materials designers with a relatively narrow processing window for making the seals.
We will review the desirable properties for glasses designed for hermetic seals between Y-stabilized zirconia (YSZ) electrolytes and oxidation-resistant Cr-Fe interconnect alloys and will discuss the relationships between glass composition and structure that help determined the desirable properties. Highly depolymerized alkaline earth/zinc silicate structures have the viscosity characteristics necessary to form a seal at 800-850°C and then be crystallized to form thermo-chemically stable glass-ceramics with the requisite thermal expansion characteristics for these seals. Studies of the long-term interfacial reactions between the glass-ceramics and the interconnect alloys will be reviewed.
