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Abstract
New insights are presented on the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 μm) and water atomised (WA, <45 μm) stainless steel AISI 316L powders. X-ray photoelectron and Auger electron spectroscopy, scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidised manganese was strongly enriched in the outermost surface oxide of the GA powders (13 and 47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enriched in oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powder surface. Tri- or tetravalent manganese oxides were observed on the GA particles in addition to α-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of a silicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr, which was confirmed not present as chromate.
Experimental help from Oskar Karlsson generating SEM images [Unit for metallic microstructure characterisation (MEMIKA), a joint facility between KTH and Swerea-KIMAB, Stockholm, Sweden], financial support by Cusanuswerk, Germany (for Yolanda Hedberg), and theoretical calculations by Johan Bratberg (Thermo-Calc assessment, Stockholm, Sweden) and invaluable discussions with Dr Olle Grinder are highly acknowledged. Yolanda Hedberg and Inger Odnevall Wallinder are members of the Stockholm Particle Group, an operative network between three universities in Stockholm: Karolinska Institutet, Royal Institute of Technology and Stockholm University, supported by the Swedish Research Councils VR and Formas.