Improving sealing properties of CaO-SrO-Al2O3-SiO2 glass and glass-ceramics for solid oxide fuel cells: Effect of La2O3 addition

Abstract

The La2O3-doped CaO-SrO-Al2O3-SiO2 glasses were prepared by the melting method. The main IR absorption peaks shift to the low wavenumber direction after the introduction of La2O3, which indicates that the amount of non-bridged oxygen in the glasses increases and the glass network depolarizes. With the increase of La2O3 content, the micro-hardness, glass transition temperature, and crystallization temperature show an increasing trend. The mass loss of acid and alkali resistance is less than 0.5 wt%, which does not affect the sealing effect of the fuel cells. The glasses were nucleated at 850 °C for 2 h and crystallized at 1050 °C for 1 h. The precipitated crystal phases of the glass-ceramics were mainly composed of SrAl2Si2O8, Ca2Al2SiO7, and CaSrAl2SiO7. As the amount of La2O3 reaches 2.5 mol%, the new crystal phase Ca3La6(SiO4)6 appears in the glass-ceramic. Ca3La6(SiO4)6 crystals liberate much more SiO2 (in comparison to other crystals) leaving Al2O3 on the border that can results in CTE increase since Al2O3 has a significantly higher CTE in compare to SiO2. The CTE of the glass-ceramics varies within the range of 9.3–11.3 ± 0.1 × 10-6 °C-1. Generally, the La2O3-doped 25CaO-20SrO-10Al2O3-45SiO2 sealing glasses have the thermal expansion coefficients similar to that of other SOFCs components.