Surface characterisation of fine inert gas and water atomised stainless steel 316L powders: formation of thermodynamically unstable surface oxide phases

New insights are presented on the speciation of surface oxide phases on fine inert gas atomised(GA, ,45 and ,4 mm) and water atomised (WA, ,45 mm) stainless steel AISI 316L powders. Xrayphotoelectron and Auger electron spectroscopy, scanning electron microscopy, Ramanspectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidisedmanganese was strongly enriched in the outermost surface oxide of the GA powders (13 and47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enrichedin oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powdersurface. Tri- or tetravalent manganese oxides were observed on the GA particles in addition to a-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of asilicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr,which was confirmed not present as chromate