Sealing behaviour of glass-based composites for oxygen transport membranes

In this study, seven different filler materials in different proportions were added to a Ba-Ca-Si glass matrix “H” to investigate new sealant with higher thermal expansion coefficient (CTE) value and good sealing performance for application in oxygen transport membrane (OTM). SrTi0.75Fe0.25O3-δ (STF25) was used as an OTM, and the sealing partners were ferritic steel Aluchrom and pre-oxidized Aluchrom. Compatibility tests were carried out to investigate the feasibility of the composites. Higher CTE values were found in dilatometer tests on composite samples by adding 40 wt% Ag (HAg40) and 30 wt% Ni-Cr (HNC30). Gas-tightness measurements of sandwiched samples produced appropriate helium leakage rates in the range of 10−6 mbar·l·s−1. Sealing behaviour of sealants HAg40 and HNC30 were investigated by joining STF25 and as-delivered/pre-oxidized Aluchrom together. Scanning electron microscopy (SEM) on cross-sections of the joints revealed a homogeneous microstructure and good adherence of the glass sealants to support metals and STF25

Thermal properties and joinability investigation of BaO–SrO–SiO 2 –B 2 O 3 glasses for oxygen transport membrane application

Three new BaO–SrO–SiO2–B2O3 (BS) glasses with different SrO contents (6–25 mol%) are developed for oxygen transport membrane (OTM) joining application. The content of strontium is investigated first in terms of its effect on the glass-forming tendency, thermal expansion coefficient, crystallization, shrinkage behavior, and viscous flow properties. Differential scanning calorimetry (DSC) is carried out. Dilatometric tests are performed to obtain coefficients of thermal expansion (CTEs) of BS glasses. The crystallization behavior of the BS glasses is investigated by X-ray powder diffraction (XRD). Sinking dilatometric measurements simulate the joining procedure and observe the shrinkage behavior of the BS glasses. The viscous flow behavior of the BS glasses is examined via hot stage microscopy. The glass with 15 mol% SrO (BS15) glass shows the best glass-forming tendency, most matching CTE (11.9 × 10−6 K−1), densest microstructure, highest shrinkage rate (24%), and good viscous behavior at high joining temperatures compared with other BS glasses. BS15 glass is chosen for helium leak test and assembly test joining with Aluchrom and SrTi0.75Fe0.25O3−δ membrane (STF25). The sandwiched sample with two Aluchrom plates sealed by BS15 glass at 1075 °C for 5 min achieves good gas-tightness with low helium leakage rate <10−9 mbar·l s−1

Thermo-Mechanical Stability and Gas-Tightness of Glass-Ceramics Joints for SOFC in the System MgO-BaO/SrO-B2O3-SiO2

The objective of this paper is to illustrate a variety of studies carried out to improve the quality of some particular glass-ceramic joining materials based on measured properties such as gas-tightness and mechanical resistance and demonstrate the feasibility of using the proposed materials for solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC) applications. First, the sealing conditions have been optimized for the two selected compositions in the system MgO-BaO/SrO-B2O3-SiO2. Once the joining materials have been optimized, the gas-tightness has been measured as a function of the glass-ceramic crystallization degree, its thermal cycling behavior and the influence of a reducing atmosphere on this property. The electrical resistance at high temperature has also been studied. Subsequently, the chemical compatibility of the joints steel/glass-ceramic has been evaluated by means of the analysis of the cross-sections using SEM and EDX. Furthermore, the mechanical and chemical stability of the joints has also been studied as a function of the crystallization degree, the resistance vs. thermal cycling and the influence of a reducing atmosphere. Finally, the mechanical resistance of the joints regarding flexural loading has been characterized employing a 4-point bending method both at room temperature and at relevant high temperatures varying the seal thickness. Overall, the results verify that the developed and tested materials are promising for long term stable SOFC and SOEC applications in advanced stack designs aiding prolonged lifetime under thermal-cyclic conditions