Fabrication of a Novel BaCe0.8Y0.2O3-δ - Cu Ceramic-Metallic Composite Membrane for Hydrogen Separation
The BCY skeleton fabrication begins with mixing appropriate amounts of BaCO3, CeO2, and Y2O3 powders with a mortar and pestle, followed by calcination in air. The phase-purity of the resulting powder is verified by X-ray diffraction spectroscopy. Binder is added to the powder via wet-milling with water, followed by pan drying. The powder is crushed with a mortar and pestle, and sieved to achieve a uniform particle size distribution. Pellets are formed by uniaxial dry-pressing, and subsequently sintered at 1600 °C in air, creating a skeleton with approximately 50 % open porosity (Figure 1a).
This porous BCY skeleton is then infiltrated with copper. Cu and CuO powders are mixed with a mortar and pestle to form a powder containing 8 at.% O. This powder is uniaxially pressed into pellets, which are placed on top of the BCY skeleton. The skeleton and Cu-CuO pellet are placed into a controlled-atmosphere furnace, and heated to 1200 °C in a 330-ppm-oxygen environment (balance argon). Under these conditions, the liquid Cu spontaneously infiltrates the BCY skeleton. While dwelling at 1200 °C, the gas environment is changed to a 10 mol.% hydrogen environment (balance argon), and the sample is cooled.
Cu will not wet, nor infiltrate, a BCY skeleton in a reducing environment, which necessitates the initial heating in the oxidizing environment. Once the Cu-CuO alloy infiltrates the BCY skeleton at high temperature, the environment can be switched to a reducing environment without the Cu-CuO alloy defiltrating the BCY skeleton, due to capillary pressure. The reducing environment removes the O from the alloy, leaving pure Cu metal. An electron micrograph of a polished-cross section of the resulting membrane (Figure 1b) reveals that the cermet is nearly fully dense. Our current efforts focus on hydrogen permeation measurements through these novel cermets.