Characteristics of Surface Oxides: Similarities and Differences between Gas and Water Atomized Steel Powders

Any metallic surface exposed to the air or any other atmosphere even with trace amount of oxygen is inevitably covered by metal oxide layer at room temperature. Hence, taking into account specific manufacturing process during both water and gas atomisation and high surface area of the powder particles, risk of surface oxide formation is significant. At the same time, usefulness of a powder is determined by the amount of oxides, their composition and spatial distribution within a metal particle. Hence, possibilities of the qualitative and quantitative analysis of powder surface chemistry by a variety of advanced spectroscopic techniques are summarised, including X-ray photoelectron spectroscopy (XPS), Auger spectroscopy and high-resolution scanning electron microscopy (HR SEM) coupled with energy dispersive X-ray analysis (EDX). The dependence of surface products composition on the alloying elements content and atomisation method is described. In both cases the metal particles are covered by heterogeneous oxide composed of particulate features of stable oxides (Cr-Mn-Si) and homogeneous iron surface oxide layer in between