Synthesis and characterization of Fe/Co/Ni alloys MgO nanocomposite powders

A mixed oxalate beta-Mg0.896Fe0.047Co0.034Ni0.023C2O4. 2H(2)O of well controlled size and morphology was prepared by coprecipitation. The corresponding quaternary solid solution between MgO, FeO, CoO and NiO was prepared by thermal decomposition and calcination in a H-2/H2O/N-2 atmosphere. The selective reduction of the solid solution in an H-2 atmosphere was studied by a combination of X-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy and associated analysis. This work has brought to light the very high stability of Fe2+, Co2+ and notably Ni2+ when substituted for Mg2+ in the MgO rocksalt lattice. It is necessary to perform the reduction at 1300 degrees C fully to reduce the transition metal ions. The alloy particles are either distributed as relatively large particles (tens to hundreds of nanometers) at the surface of the MgO grains or as much smaller particles (less than or equal to 20 nm) probably located inside the matrix grains and epitaxial with it. The composition distribution of the large surface particles is fairly broad when the reduction was performe at 1100 and 1300 degrees C. In contrast, it is much narrower in the powder prepared by reduction at 1200 degrees C, although the particles are still low in Ni compared to the target composition.