Atmospheric-pressure Microwave Torch Discharge Generated γ-Fe2O3 Nanopowder

Abstract

Microwave torch discharge ignited in Ar at 1 bar was used for the synthesis of gamma-Fe2O3 nanoparticles. A double-walled nozzle electrode enabled to introduce gases separately: Ar flowed in the central channel, whereas the mixture of H-2/O-2/Fe(CO)(5) was added into the torch discharge through an outer channel. The composition and properties of the synthesized nanopowders were studied by TEM, XRD, Raman and Mossbauer spectroscopies. Basic magnetic measurements at low/high temperatures were performed. The gamma-Fe2O3 phase with the mean crystallite size of 24 nm was identified by XRD in the representative sample. The measured Raman spectrum matched well those reported for gamma-Fe2O3 powders in the literature. In the transmission Mossbauer spectrum measured at 5 K the two sextets characteristic for gamma-Fe2O3 were clearly identified. No change in specific magnetic moment typical of Fe3O4 at its Verwey temperature was observed on the zero field curve, which smoothly increased with temperature. Neither Fe3O4 nor alpha-Fe2O3 were present in the sample. We also report on the high-temperature magnetic properties of the representative sample and describe its structural changes and phase transformations up to 1073 K.