Silver-palladium submicronic powders

The structure of new submicronic spherical Ag-Pd powders (75/25 and 70/30 wt/wt% as spheres of mean diameter ca. 300 nm) has been investigated by various techniques. X-ray diffraction, carried out on both powder and single particles, showed two distinct metal phases, the first one being pure silver, the second one slightly alloyed palladium. X-ray microanalysis performed under SEM indicated that each grain displays intermetallic character, both metals being present in proportion close to the mean composition. Space-resolved information has been obtained by three different techniques: X-ray microanalysis carried out under transmission electron microscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry, the three of them leading to converging results. Each grain appears as a core made of pure silver surrounded by a 10–15 nm thick layer of slightly alloyed palladium with a mean Pd/Ag ratio 89%/11% which possibly increases from inside to outside.