Trends in wetting behavior for Ag–CuO braze alloys on Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O (32d) at elevated temperatures in air Vineet V. Joshi • Alan Meier • Jens Darsell • K. Scott Weil • Mark Bowden Received: 9 April 2013 / Accepted: 12 June 2013 / Published online: 21 June 2013 Ó Springer Science+Business Media New York 2013 Abstract In the current study, Ag–CuO, a reactive air brazing alloy was evaluated for brazing Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O (3-d) (BSCF). In situ contact angle tests were per- formed on BSCF using Ag–CuO binary mixtures at 950 and 1000 °C, and the interfacial microstructures were evaluated. Wetting contact angles (h \ 90°) were obtained at short times at 950 °C, and the contact angles remained constant at 1000 °C for 1, 2, and 8 mol% CuO contents. Microstructural analysis revealed the dissolution of copper oxide into the BSCF matrix to form copper–cobalt–oxygen rich dissolution products along the BSCF grain boundaries. The formation of a thick interfacial reaction product layer and ridging at the sessile drop triple point indicate that the reaction kinetics are very rapid and that it will require careful process control to obtain the desired thin but con- tinuous interfacial product layer. Introduction In order to facilitate high-efficiency carbon capture in the next generation of coal-based power plants, the development of oxy-combustion and integrated gasification combined cycle (IGCC) technologies is presently under development [1, 2]. These technologies rely on a supply of high-purity oxygen to the combustion units in order to efficiently gen- erate CO 2 and minimize the emission of other gases. Cur- rently, prototypes are being developed based on cryogenic separation of air to deliver pure oxygen. However, this approach is energy intensive and accounts for more than 10 % of the energy loss. An alternative, more efficient gas separation methodology is to use a solid state device based on mixed ionic/electronic conducting (MIEC) ceramic mem- branes. These membranes selectively catalyze the dissocia- tion of oxygen from air on one side, and transport it across a chemical gradient to the other side. This type of MIEC separation system is responsible for only a 2–5 % efficiency loss, and thus, it has been considered as a potential technique for oxygen separation [1–6]. For efficient transport of oxy- gen, these membranes usually operate at elevated tempera- tures in the range from 600 to 1000 °C[1, 2]. Cobaltites or cobalt-based perovskite MIECs provide a high-oxygen flux as compared to the other perovskite and fluorite structures. These cobaltites have a coefficient of thermal expansion (CTE) of approximately 17 9 10 -6 K -1 at elevated temperatures. The development of oxygen sepa- ration membranes requires a manifold material that is not only stable at an elevated temperature for long periods of time but also closely matches the cobaltites CTE [1–3]. Face centered cubic (FCC) nickel-based alloys have CTE’s between 14 and 18 9 10 -6 K -1 and are thus compatible with these systems [6, 7]. Pfaff and Zwick [6] recently evaluated the available MIEC membrane materials in depth and selected V. V. Joshi  A. Meier Kazuo Inamori School of Engineering, Alfred University, Alfred, NY, USA Present Address: V. V. Joshi (&) Pacific Northwest National Laboratory, Richland, WA, USA e-mail: vineet.joshi@pnnl.gov Present Address: A. Meier Department of Metallurgical and Materials Engineering, Montana Tech of the University of Montana, Butte, MT, USA J. Darsell  K. S. Weil  M. Bowden Pacific Northwest National Laboratory, Richland, WA, USA Present Address: K. S. Weil Owens-Illinois, Perrysburg, OH, USA 123 J Mater Sci (2013) 48:7153–7161 DOI 10.1007/s10853-013-7531-2