Improved Wetting of Mixed Ionic/Electronic Conductors Used in Electrochemical Devices with Ternary Air Braze Filler Metals

Abstract

This paper reports on the wetting behavior, reactivity, and long-term electrical conductance of a series of ternary filler metals being considered for brazing lanthanum strontium cobalt ferrite (LSCF)-based oxygen separation membranes. Mixed ionic/electronic conducting perovskite oxides such as LSCF and various doped barium cerates are currently being considered for use in high-temperature electrochemical devices such as oxygen and hydrogen concentrators and solid oxide fuel cells. However, to take full advantage of the unique properties of these materials, reliable joining techniques need to be developed. Furthermore, if the proposed joining technique were to yield a hermetic ceramic-to-metal junction that was also electrically conductive, it would additionally benefit the device by allowing current to be drawn from or carried to the electrochemically active mixed conducting oxide component without requiring a separate current collector. A newly developed brazing technique known as air brazing is one such method of joining. In its present form, air brazing uses a silver-copper oxide based filler metal that can be melted directly in air to form a compliant joint that is electrically conductive. Recently, it has been shown that the addition of titania can enhance the wetting behavior of filler metals on alumina. Here the effect of this wetting agent on the surface wettability, long-term electrical resistance at , and reactivity with (LSCF-6428 or LSCF) substrates is discussed.