Investigation on Glasses in Strontium Zinc Borosilicate System as Sealants for Solid Oxide Fuel Cell
Glasses in the SrO-ZnO-B2O3-SiO2 (SZBS) system with different additives like V2O5, Cr2O3, TiO2, and Al2O3 have been prepared by melt-quench method. Glasses were subjected to controlled heat treatment for conversion into glass-ceramics. Investigated glasses and glass-ceramics have thermal expansion coefficients (TEC) in the range of 95-120 x 10-7/oC (30-600 oC) which closely match with TEC of other SOFC components. XRD indicates the crystallization of Sr2ZnSi2O7 solid-solution phase in glasses upon heat treatment. Structural studies revealed that mainly Q1 and Q2 silicate structural units are present in the glass network and B2O3 enters in the network as triangular borate (BO3) structural units. Only small fraction of B2O3 enters as tetragonal borate (BO4) structural units at higher concentration of B2O3. Glass network depolymerizes with the addition of additives and concentration of Q1 units increases at the expense of Q2 units. Small addition of V2O5 in SZBS glass is beneficial for increasing TEC and achieving better flowability at lower sealing temperature. Studied SZBS glasses also show good bonding with Crofer-22-APU. Elemental line scans indicate that interdiffusion of Fe, Cr, Sr and Si across interface is responsible for good bonding with Crofer-22-APU. To show suitability of material for high temperature sealing, seals have been prepared and tested for vacuum integrity at 850oC for 500h.
B.S.S. Daniel and G.P. Chaudhari
B. Tiwari et al., "Investigation on Glasses in Strontium Zinc Borosilicate System as Sealants for Solid Oxide Fuel Cell", Advanced Materials Research, Vol. 585, pp. 195-199, 2012