Atmospheric Non-thermal Plasma Reduction of Natively Oxidized Iron Surfaces

Abstract

Plasma in hydrogen-containing atmospheres is an efficient method for the reduction of iron oxides. Although a vast number of approaches were performed for the reduction of bulk Fe oxides with thermal hydrogen plasmas, there is almost no information about the non-thermal plasma reduction efficiency in the atmospheric pressure range. In the current article we present the reduction of natively oxidized iron surfaces applying a dielectric barrier discharge plasma in an Ar/H2 atmosphere at 1000 hPa. By varying the surface temperature from 25 to 300 °C, we studied the plasma reduction efficiency, which was then compared with a thermal method. Whereas plasma treatments at 25 °C and 100 °C did not result in the significant reduction of iron oxidized species, experiments at 200 °C and 300 °C yielded a reduction of approximately 88% and 91% of initial oxidized components already after 10 s, respectively. Moreover, we observed an increase in the efficiency with a plasma-thermal reduction in comparison to a thermal method, which was attributed to the presence of atomic hydrogen in the plasma phase. Analysis of morphology revealed the formation of Fe–C structures on surfaces after thermal and plasma-thermal treatments at 200 °C and 300 °C that may be connected with the diffusion of bulk contaminations to the deoxidized surface and reactions between the reduced Fe with plasma-activated adventitious carbon. Conclusively, the plasma was characterized by analyzing the reactive species and the electron temperatures.