On the chemical stability of iron-nitride magnetic fluids in atmospheric conditions

The chemical stability of iron-nitride magnetic fluids prepared by coating titanium and cobalt has been assessed in an atmospheric condition by means of measurements on their saturation magnetizations and mass changes. The mass changes of both the uncoated and coated iron-nitride magnetic fluids gradually increased on exposing to an atmosphere. Saturation magnetizations of iron nitride magnetic fluids decrease with increasing exposure time, and approach zero after 1008 h of exposure time. Such changes are probably caused by an oxidation of iron-nitride particles. The final oxidation form of iron nitride at room temperature is considered to be non-magnetic hematite (alpha-Fe2O3) rather than ferromagnetic magnetite (Fe3O4) and/or maghemite (gamma-Fe2O3). It has been found that cobalt prevents the oxidation of iron-nitride particles in the initial moments of exposure time. (C) 1999 Elsevier Science B.V. All rights reserved.