Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn0.5Ni0.5Fe2O4/Fe type were synthesized starting from nanocrystalline Mn0.5Ni0.5Fe2O4 (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn0.5Ni0.5Fe2O4/Fe, were milled for up to 120 min and subjected to heat treatment at 600 A degrees C and 800 A degrees C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 A degrees C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn0.5Ni0.5Fe2O4/Fe composite are stable up to 400-450 A degrees C. In the temperature range of 450-600 A degrees C, the interdiffusion phenomena occurs leading to the formation of Fe1-xMnxFe2O4/Ni-Fe composite type. The new formed ferrite of Fe1-xMnxFe2O4 type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 A degrees C and 800 A degrees C). The mean crystallites size of the ferrite after heat treatment at 800 A degrees C is about 75 nm. After DSC treatment at 900 A degrees C, the composite material consists in Fe1-xMnxFe2O4, Ni structure, FeO, and (NiO)(0.25)(MnO)(0.75) phases.