Study of Microwave Torch Plasmachemical Synthesis of Iron Oxide Nanoparticles Focused on the Analysis of Phase Composition

Abstract

This work presents the results obtained on the single-step route towards the synthesis of iron oxide nanoparticles in a microwave plasma torch. The torch is supplied by 660 sccm of Ar mixed with 1 sccm of Fe(CO)5 and a variable amount of O2. The influence of oxygen addition on the phase composition of the synthesized powder was studied. Magnetite and maghemite phases could not be distinguished using the standard X-ray diffraction (XRD) analysis. Therefore, a combined XRD and Raman spectra analysis had to be applied, which is based on fitting of selected diffraction peaks and spectral features. According to XRD and Raman spectroscopy, the powder synthesized from Ar/Fe(CO)5 consisted about 50 % of magnetite, Fe3O4, the rest being α-Fe and FeO. An increase in oxygen flow rate led to an increase in γ-Fe2O3 percentage, at the expense of α-Fe, FeO and Fe3O4. Almost pure γ-Fe2O3 was synthesized at oxygen flow rates 25–75× higher than the flow rate of Fe(CO)5. A further increase in the oxygen flow rate led to α-Fe2O3 and e-Fe2O3 production. The distributions of nanoparticles’ (NPs) diameters were obtained using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The mean diameter of the NPs measured by TEM was 13 nm while the DLS measurements led to the mean diameter of 12 nm. About 90 % of all particles had the diameter in the range of 5–21 nm but a few larger particles were observed in TEM micrographs.