Fine-tuning the feature size of nanoporous silver

We show that the characteristic ligament size of nanoporous Ag synthesized by chemical dissolution of Al from Ag-Al alloys can be tuned from the current submicrometer size (similar to 100-500 nm) down to a much smaller length scale (similar to 30-60 nm). This is achieved by suppressing the formation of the Ag2Al intermetallic compound in the alloy precursor

Ordering of Octahedral Vacancies in Transition Aluminas

The microstructure of transition aluminas obtained via the dehydration of boehmite has been characterized by using transmission electron microscopy (TEM). The presence of γ-, δ-, and θ-aluminas was identified by using selected-area electron diffraction. Modifications that resulted from the reordering of aluminum vacancies on octahedral sites in a cubic close-packed oxygen network have been detected and analyzed by using high-resolution transmission electron microscopy (HRTEM) combined with image simulations. A good correspondence of the observed and calculated images confirmed the ordering of vacant octahedral sites located on {011} and {011¯} planes that formed a zigzag configuration along the direction. Two more arrangements of empty octahedral sites, but now concentrated on {001} planes, have been determined in the sintered powder-gel agglomerates. Structure analysis suggested that the modifications are all associated with the rearrangement of vacant sites during the phase transformation from γ-alumina to δ-alumina, and further to θ-alumina, and may be driven by configuration entropy minimization