Selective oxidation of surface grains in polycrystalline tin

Polycrystalline tin samples have been imaged during oxidation with molecular oxygen using the scanning photoelectron microscope on beam line 2.2 at the ELETTRA synchrotron. Chemical maps have been recorded by collecting the Sn 3d signal from the metal and oxide phases. The reactivity of surface grains, as indicated by the oxide signal, depended on the crystal plane exposed. In the early stages of oxidation studied here only SnO was formed. The reactivities of different grains judged from images and from the spectra taken on selected microspots have been used to suggest identifications for the crystal planes involved.