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

Abstract

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-B 2 O 3 -SiO 2 . 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.

Review on silicate and borosilicate‐based glass sealants and their interaction with components of solid oxide fuel cell

“…30 The creep behavior of glass sealants/interconnect has been reported at high temperature by many researchers. [31][32][33] Normally, creep cracks initiate at the interfaces and fast fracture takes place within the glass-ceramic sealant. 33 Also, the creep behavior of glass-ceramic reduces the height of fuel flow channels.…”

“…Another most important criterion is the glass transition temperature ( T g ) above which the materials change from brittle to ductile behavior and some structural inabilities may occur 30 . The creep behavior of glass sealants/interconnect has been reported at high temperature by many researchers 31–33 . Normally, creep cracks initiate at the interfaces and fast fracture takes place within the glass‐ceramic sealant 33 .…”

“…Rodriguez-Lopez et al have reported the gas tightness of glass sealant (27SrO-18MgO-10B 2 O 3 -45SiO 2 ) with interconnect. It showed good gas tightness at 850 C. 31 MgO-containing glasses Overall, multicomponent glasses exhibit complex crystallization during heat treatment. 200 However, it seems that MgO [201][202][203] containing glass sealants are more complicated than other alkaline earth metal oxide-containing glasses since a large number of crystalline phases are formed, many of them being meta-stable, which can convert into more stable counterpart during a longer period of the heat treatment of SOFC operation.…”

“…The developed and tested materials could be promising for long-term stable SOFC and Solid oxide electrolyzer cells (SOEC) applications. 31 However, the BaO-containing glass sealant required high temperature for sealing to achieve proper gas tightness due to its higher crystallization rate with high viscosity and poor wettability to adhere with interconnecting materials. 31 CaO-containing glasses Many researchers [160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176] have investigated the crystallization of CAS (CaO-Al 2 O 3 -SiO 2 ) glasses.…”

Effect of electrolyte thickness manipulation on enhancing carbon deposition resistance of methane‐fueled solid oxide fuel cell

“…There were studies supported that the sample is considered gas-tight when the gas permeance value does not exceed 10 −5 to 10 −6 mol m −2 s −1 Pa −1 . 13,28,29 The high sinterability of YSZ helped to achieve dense electrolyte layer. 25 Additionally, optimum electrolyte thickness might also be one of the main contributor to the gas-tightness property of that layer.…”