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 ma ss changes of both the uncoated and coated iron-nitride magnetic fluids gra dually increased on exposing to an atmosphere. Saturation magnetizations of iron nitride magnetic fluids decrease with increasing exposure time, and a pproach zero after 1008 h of exposure time. Such changes are probably cause d by an oxidation of iron-nitride particles. The final oxidation form of ir on nitride at room temperature is considered to be non-magnetic hematite (a lpha-Fe2O3) rather than ferromagnetic magnetite (Fe3O4) and/or maghemite (g amma-Fe2O3). It has been found that cobalt prevents the oxidation of iron-n itride particles in the initial moments of exposure time. (C) 1999 Elsevier Science B.V. All rights reserved.