Enhanced oxidation of Fe3O4 using CO2 plasma and production of Υ-Fe2O3

Abstract

Iron oxides have been widely used as materials in various fields, and among them, maghemite has gained significant attention due to its magnetic properties and specific structure. The fabrication processes of iron oxides with these desirable characteristics have been extensively investigated. In this paper, we propose a method for enhancing the oxidation of magnetite to maghemite by combining atmospheric pressure microwave carbon dioxide (CO2) plasma with laser heating. This approach aims to enhance oxidation and achieve the production of maghemite through the reactive species in the CO2 plasma and efficient surface heating by the laser.

To demonstrate the concept, magnetite powders were prepared in the form of easily analyzable pellets. The effects of various CO2 plasma concentrations, surface temperatures, and distance between electrodes and samples have been investigated. The surface of the samples was analyzed using Raman spectroscopy, and the particle size before and after the reaction was compared using scanning electron microscopy. The reactive species in the plasma were assumed to be oxygen atoms and used as indicators.

The surface of the magnetite pellets was found to be oxidized to maghemite or hematite depending on the temperature, regardless of the gas ratio. While an increase in the peak intensity of oxygen atoms indicated an improvement in the oxidation of magnetite, an overall increase in peak intensity was observed in all regions, suggesting that factors other than oxygen atoms also influenced the reaction. It was determined that the decomposition of CO2, particularly in the region close to the electrode and the sample surface temperature, played crucial roles in enhancing oxidation through plasma treatment. Furthermore, the optimal temperature for maghemite production is around 570K, and it is effective in producing maghemite because the hematite formation was not observed on the surface.