Status of Refractory Sealing Glass Development at PNNL: Effect of Aluminization on the Mechanical Strength and Electrical Stability

A novel series of alkaline earth based silicate sealing glass was developed at Pacific Northwest National Laboratory (PNNL) for SOFCs to be sealed at higher temperatures.  Earlier studies showed undesirable chromate formation at glass/metal interfaces exposed to air.  Remedies were sought by aluminizing metallic interconnect in reducing environment followed by oxidation to promote a thin layer of Al₂O₃.  Small aluminized metal coupons (1/2”x1/2”) were sealed with refractory glass and tensile strength was tested.  In addition, the sealed couples were also aged at 850^oC/300h in different environment.  Results of tensile strength showed no strength degradation at all for samples aged in air as well as in reducing environment.  The aluminized samples were also subjected to electrical stability test with a DC 0.7V across the seal at 850^oC.  Microstructure and elemental analyses along glass/metal interfaces will be characterized and discussed.