Thermal behavior and crystallization of alkali aluminosilicate sealants for SOFC: Effect of Al2O3 to Y2O3 substitution

The influence of the gradual replacement of Al₂O₃ with Y₂O₃ in alkali-containing silica glass sealants is studied with a detailed discussion of crystallization kinetics. Such substitution has a complex effect on T_g, T_sphere, T_HS, and T_flowing which might be connected with the role of yttrium in the glass network. An increase in the Y₂O₃ content is found to intensify crystallization, causing the growth of the crystalline phase fraction. At the same time, intense crystallization appears to have no pronounced effect on the coefficient of thermal expansion: its average increment after 1000 h of exposure at 850 °C in air atmosphere is <1‧10⁻⁶ K⁻¹. The only crystalline phase observed in samples with Y₂O₃ content greater than 2 wt % is suggested to be Na_0.8Ca_0.3Y_0.4Zr_0.22Si_2.13O₆ which is the Ca²⁺- and Zr⁴⁺-substituted isomorph of NaYSi₂O₆.