Influence of long-term thermal treatment of magnetite nanoparticles on its physicochemical properties

In the presented paper, a long term thermal treatment at 50 °C was performed on four types of magnetite nanoparticles to observe if there is a transformation induced to other iron oxides. Such information is critical when hyperthermia application is foreseen due to different magnetic properties of Fe ₃O ₄, γ-Fe ₂O ₃ and α-Fe ₂O ₃ . Nanoparticles were obtained by co-precipitation of iron (II) and (III) chlorides or by thermal decomposition of iron (III) acetylacetonate. Both types of nanoparticles were covered with a protective silver shell to increase their oxidative stability. The experiment was conducted in phases over the course of 28 days. Characterization of thermally treated nanoparticles was performed by transmission electron microscopy, x-ray diffraction, infrared spectroscopy and Mössbauer spectroscopy. According to the obtained results, nanoparticles synthesized by co-precipitation of iron chlorides are less thermally stable than those obtained by thermal decomposition. However, both types of nanoparticles do not oxidize to hematite even when exposed to long-term (up to 28 days) gentle (below 50 °C) heating.