An Ag based brazing system with a tunable thermal expansion for the use as sealant for solid oxide cells

Abstract

An Ag-Al 2 TiO 5 composite braze was developed and successfully tested as seal for solid oxide cells. The thermo-mechanical properties of the Ag-Al 2 TiO 5 system and the chemical compatibility between this composite braze and relevant materials used in stacks were characterized and the leak rates as a function of the operation temperature were measured.The thermal expansion coefficient in the Ag-Al 2 TiO 5 system can be tailored by varying the amount of the ceramic filler. The brazing process can be carried out in air, the joining partners showed a good chemical stability and sufficient low leak rates were demonstrated. Furthermore, the long-term stability of the Ag-Al 2 TiO 5 composite braze was studied under relevant SOFC and SOEC conditions. The stability of brazed Crofer/ Ag-Al 2 TiO 5 /NiO-YSZ assemblies in reducing atmosphere and in pure oxygen was investigated over 500 h at 850 °C.Additionally, a cell component test was performed to investigate the durability of the Ag-Al 2 TiO 5 seal when exposed to dual atmosphere. The seals performed well over 900 h under electrolysis operation conditions (-0.5 A cm 2 , 850 °C), and no cell degradation related to the Ag-Al 2 TiO 5 sealing was found, indicating that the developed braze system is applicable for the use in SOFC/SOEC stacks.

In‐situ synthesis of TiC nanoparticles during joining of SiC ceramic and GH99 superalloy

“…18,28,29 In order to investigate the effects of GNPs with a flake-like structure on wettability of brazing filler metal, the wetting experiment of AgCuTi-1 wt.% GNPs composite filler on SiC ceramic surface was performed. 18,28,29 In order to investigate the effects of GNPs with a flake-like structure on wettability of brazing filler metal, the wetting experiment of AgCuTi-1 wt.% GNPs composite filler on SiC ceramic surface was performed.…”

“…The combine of particles or fibers and brazing alloy was reported to deteriorate the wetting performance. 18,28,29 In order to investigate the effects of GNPs with a flake-like structure on wettability of brazing filler metal, the wetting experiment of AgCuTi-1 wt.% GNPs composite filler on SiC ceramic surface was performed. Especially, the wettability of AgCu and AgCuTi filler were served as the contrast experiments.…”

Commercial alkaline earth boroaluminosilicate glasses for sealing solid oxide cell stacks. Part I: Development of glass‐ceramic microstructure and thermomechanical properties

“…These numbers are interesting when glasses are used as sealants between steel and SOCs to assess thermomechanical properties of the joints. The range, RT‐800°C, was selected based on conventional operating temperatures for SOC‐stacks, which are between 750°C and 820°C, and it may be noted that both MCAS and cf11 attained T‐CTE, which are close to the T‐CTE of the anode supported cell, 10‐12 × 10 −6 K −1 and of commonly used ferritic steels for interconnector, T‐CTE 10‐13 . Maximum values for the T‐CTE were in general positioned around 240°C, not included in Table , and at 600‐700°C, reflecting contents of cristobalite and residual glass, respectively.…”

“…The very same mechanism is probably also responsible for differences in both the amount of residual glass and the phase assemblages observed between eg cf11 and MCAS, cf Figure , and causes the differences in high temperature properties between the two, namely that MCAS in contrast to cf11 tend to yield above 800°C, thus providing better performance, if a self‐healing sealant is wished for, cf (Figure ). The figure also depicts that the technical CTE between room temperature and 800‐850°C is maximized for the MCAS‐sealant, spanning to 10.5 × 10 −6 K −1 , presumably due to the relatively high concentration of both cristobalite, quartz, and vitreous phases thus providing the best thermomechanical match among the candidates towards counterparts of SOCs (CTE: 12.6 × 10 −6 K −1 ) and metallic interconnects of eg Crofer 22APU (CTE: 12.3 × 10 −6 K −1 ) …”

Investigation of a Spinel‐forming Cu‐Mn Foam as an Oxygen Electrode Contact Material in a Solid Oxide Cell Single Repeating Unit

“…The SRU test setup is shown in Figure . For further information see , . The SRU was heated up to 900 °C for sealing with 20 NL h −1 of 9% H 2 in N 2 supplied to the fuel electrode and 40 NL h −1 of air supplied to the oxygen electrode.…”