Thermal evolution of the Ni-ferrite nanoparticles obtained by mechanical alloying as probed by differential scanning calorimetry

An investigation of the formation of Ni-ferrite from a powder mixture of NiO and Fe2O3 by high-energy ball milling combining X-ray diffraction and differential scanning calorimetry (DSC) is presented. The XRD results indicate that the NiO/Fe2O3 particles reacted in a self-sustaining combustion mode, producing nickel ferrite particles ranging from 5 to 18 nm in size after 18 h of milling. The DSC traces present a broad exothermic reaction peak at the temperature range of 200-1,000 A degrees C, with a big mountain-peak around 672 A degrees C, of the as-received powder mixture. It shifts from 672 to 647 A degrees C by increasing milling time to 18 h. The onset temperature of the transition is in the range of 736-844 A degrees C for milled samples between 6 and 18 h. The transition is assigned to the re-crystallization of the nanocrystalline samples. The Curie temperature of Ni-ferrite is also observed in the DSC traces for the 18 h-milled sample, suggesting the Ni-ferrite formation. The performed thermogravimetry for this sample indicates the no mass changes, whereas for as-received powder mixture the mass change is about 1.2 %. FT-IR spectra shows two absorption bands in the Ni-ferrite structure around 400 and 600 cm(-1), which are attributed to octahedral and tetrahedral sites, respectively.