Thermal and chemical properties of "invert" glasses and glass-ceramics developed for hermetic seals for solid oxide fuel cells are described. The glasses crystallize to form thermally stable pyro- and orthosilicate phases with the requisite thermal expansion match to the Y-stabilized ZrO2 (YSZ) electrolyte. In addition, the glasses bond to Cr-steel substrates at 800-850 °C without forming extensive interfacial reaction products. The thermal expansion characteristics of the glass-ceramics remain essentially unchanged after 28 days at 750 °C. Compositions with lower (<2 mol%) B2O3 contents exhibit the lowest volatilization rates when exposed to wet forming gas at 750 °C.