David B. Robinson

Palladium nanoparticles are functional materials that catalyze many chemical reactions involving carbon and/or hydrogen [ 1]. Their ease of preparation and resistance to bulk oxidation make them convenient for study by electron microscopy [ 2]. Hydrogen is readily absorbed into palladium and induces microstructural changes [ 3, 4]. Some of these are readily observed in the microscope [ 5], but others, such as vacancies, are more difficult to detect [ 6].

The U.S. Department of Energy's Office of Scientific and Technical Information

Chemical engineering systems often involve a functional porous medium, such as in catalyzed reactive flows, fluid purifiers, and chromatographic separations. Ideally, the flow rates throughout the porous medium are uniform, and all portions of the medium contribute efficiently to its function. The permeability is a property of a porous medium that depends on pore geometry and relates flow rate to pressure drop. Additive manufacturing techniques raise the possibilities that permeability can be arbitrarily specified in three dimensions, and that a broader range of permeabilities can be achieved than by traditional manufacturing methods. Using numerical optimization methods, we show that designs with spatially varying permeability can achieve greater flow uniformity than designs with uniform permeability. We consider geometries involving hemispherical regions that distribute flow, as in many glass chromatography columns. By several measures, significant improvements in flow uniformity can be obtained by modifying permeability only near the inlet and outlet.