Long-term thermal stability of sealing glass is critical for hermetic seals of solid oxide fuel and electrolyzer cell stacks. In this work, a SrO-La2O3-Al2O3-SiO2 glass (SABS-0 glass) has been evaluated as a high temperature sealant by thermal treatment. Powder and bulk SABS-0 glasses are studied in both air and H-2/H2O atmospheres at 800 degrees C for up to 1000 h. Weight measurements show negligible SABS-0 glass vaporization during the thermal treatment. Both SABS-0 powder and bulk samples show some surface devitrification but the SABS-0 glass bulk remains amorphous at all the thermal treatment conditions. On the polished bulk SABS-0 surface, needle-shaped crystals are observed for both the air and the H-2/H2O thermal treatment conditions. Polishing is believed to be the initiator for the SABS-0 glass surface devitrification. The crystalline phases, indentified as silicates and aluminates, increase with the thermal treatment time. However, the crystalline phases on the polished SABS-0 glass surface are very limited and only exist on the very surface of both the air and the H-2/H2O atmosphere treated samples. The SABS-0 glass has excellent thermal stability in solid oxide fuel/electrolyzer operating environments and is a promising sealant material for such applications. (C) 2009 Elsevier B. V. All rights reserved.