Gamma-Iron Phase Stabilized at Room Temperature by Thermally Processed Graphene Oxide

Abstract

Stabilizing nanoparticles on surfaces, such as graphene, is a growing field of research. Thereby, iron particle stabilization on carbon materials is attractive and finds applications in charge-storage devices, catalysis, and others. In this work, we describe the discovery of iron nano-particles with the face-centered cubic structure that was postulated not to exist at ambient conditions. In bulk, the y-iron phase is formed only above 917 ?C, and transforms back to the thermodynamically favored a-phase upon cooling. Here, with X-ray diffraction and Mossbauer spectroscopy we unambiguously demonstrate the unexpected RT stability of the y-phase of iron in the form of the nanoparticles with low carbon content from 0.60% through 0.93%. The nanoparticles have controllable diameter range from 30 nm through 200 nm. They are stabilized by a layer of Fe/C solid solution on the surface, serving as the buffer controlling carbon content in the core, and by layer graphene as an outermost shell.