A Reliable High-temperature Sealing Technology for Gas Separation Devices
Funded by U.S. Department of Energy
Project Summary
One critical technology essential for high-efficiency, low emission fossil energy conversion is the development of a reliable sealing technology that enables the hermetical joining of ceramic membranes used in high temperature gas separation to the underlying metallic support structures (e.g. metallic body) in gas separation devices and systems. This DoE SBIR project is to develop a novel class of sealing technology that can be used for sealing the ceramic membranes at high temperatures (greater than 650ºC), providing sufficient wettability, chemical inertness, thermal reliability, and bonding strength. The successful development of such a high-temperature sealing technology will enable the achievement of high efficiency, low emissions in resultant advanced energy systems.
In Phase I, Aegis, teamed with the Dr. Scott Weil’s group in the Energy Science and Technology Division of Pacific Northwest National Laboratory (Richland, Washington), has successfully carried out the technical feasibility research for the proposed sealing technology. The Phase I work covers the experimental investigations on braze filler material compositions, brazing process, extensive characterizations including microstructure analysis, wetting behaviors, mechanical properties, and preliminary hermeticity testing. In addition, a finite element model has been established to study the thermal residual stress generated during reactive air brazing (RAB).
In this Phase I project, a novel class of composite RAB braze based on Ag-CuO with additional elements of Al2O3 and TiO2 was designed, synthesized, investigated and compared in terms of wetting behaviors, microstructure, joining strength, and hermeticity. The results showed that with an appropriate composition design and processing control, the proposed composite braze demonstrated excellent joining characteristics in wetting behaviors, microstructure, joining strength, and hermeticity, showing much improved joint performance by avoiding the issues oftentimes accompanied with the use of a conventional Ag-4CuO air braze formulation. Preliminary joining practice using the proposed two-step sealing procedure was performed on alumina ceramics including porous alumina and metals (stainless steel and Fecralloy). The assemblies include ceramic tube joined to metal plate, as well as ceramic tube joined to metal tube. All of these prototypes showed good joining appearance. In addition, a preliminary FEA modeling was created to evaluate the thermal residue stress in a typical ceramic-braze-ceramic assembly during reactive air brazing.
During this Phase I development, Aegis has started discussion with Pacific Northwest National Laboratory (PNNL) and other companies to facilitate the potential commercialization of the technology into gas separation devices. In the subsequent SBIR Phase II project, Aegis will continue the material composition and processing optimizations, carry out more detailed characterizations particularly on mechanical properties at elevated temperatures, and demonstrate some typical components that can be direclty used at targeted applications including gas sepration devices and solid oxide fuel cells (SOFCs).