BaZn2Si2O7 and the solid solution series BaZn2-xCoxSi2O7 (0 < x ≤2) as high temperature seals for solid oxide fuel cells studied by high-temperature X-ray diffraction and dilatometry

For sealing of solid oxide fuel cells, glasses from which crystalline phases with high coefficient of thermal expansion (CTE) can be crystallized are required. In this paper, a new solid solution series BaZn2,Co,.. Si2O7 (0 <x 2) is introduced which exhibit extremely high CTE. The prepared powders were characterized by X-ray diffraction and high-temperature X-ray diffraction (BaZn2Si2O7). Sintered specimens were characterized by dilatometry. The introduction of Co2+ does not lead to a change in the space group. All compounds show a transition of a low to a high temperature modification. The attributed temperature increases from 300 degrees C for BaZn2Si2O7 to 850 degrees C for BaCo2Si2O7. The volume expansion which runs parallel to the phase transition decreases with increasing cobalt concentration. The phase BaZn2Si207 shows the largest CTE and a steep volume effect during phase transition. For the compound BaZn0.25C01.75Si2O7 the CTE is minimum (8.6 x 10(-6) K-1 (50-900 degrees C)) and increases again until for the compound BaCo2Si2O7 a CTE of 16.6 x 10(-6) K-1 (50-900 degrees C) is reached. In the cobalt rich Composition range, the CTEs are in the right range for high temperature fuel cells and can be adjusted by the composition. (C) 2013 Elsevier Inc. All rights reserved.