Effects of annealing on phase evolution, microstructure and magnetic properties of mechanically synthesized nickel-ferrite
Abstract The influence of milling and subsequent annealing on nickel-ferrite phase formation was investigated by X-ray diffraction (XRD). Microstructure and magnetic properties of NiFe 2 O 4 were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibration sample magnetometry (VSM). Single phase nanosized nickel-ferrite was obtained by 30 h mechanical alloying (MA) and subsequent annealing at 600 °C for 1 h. Magnetic properties of the milled powder were extensively affected by the annealing temperature. Considerable growth of the particles and necking by sintering resulted from annealing at 1000 °C.
Fe50Co50 nanoparticles via self-propagating high-temperature synthesis during milling
Abstract Self-propagating exothermic reactions during mechanical milling of FeCl 3 /CoCl 2 mixture together with sodium seeds resulted in formation of Fe 50 Co 50 nanoparticles. Highly exothermic reactions resulted in temperature raise and formation of Fe 50 Co 50 phase within the first 5 min; however Fe 50 Co 50 single-phase was obtained after 30 min of milling. The products were characterized by XRD, SEM, EDS, TEM and VSM. Obtained results showed that both milling time and NaCl salt matrix affected the size, morphology, microstructure and magnetic properties of the produced particles.
Synthesis of nickel ferrite nanoparticles by sol-gel method
Abstract NiFe 2 O 4 nanoparticles were prepared by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. It was shown that pure spinel NiFe 2 O 4 nanoparticles with a diameter of 5∼30 nm and a specific surface area of 20.0∼55.2 m 2 /g could be produced by calcining the gel precursors with various molar ratios of PAA to total metal ions (0.5∼2.0) in air at 300°C for 2h. As the molar ratio of PAA to total metal ions increased, particle sizes decreased but the crystallinity increased, revealing PAA not only worked as a chelating agent to disperse the cations homogeneously but also contributed its combustion heat to increase the crystallinity of NiFe 2 O 4 nanoparticles. Moreover, the magnetic analysis showed the resultant NiFe 2 O 4 nanoparticles might be superparamagnetic. Their saturation magnetization (0.19 emu/mol at 298 K) was slightly lower than that for bulk materials due to small size and increased slightly with decreasing the temperature below 360 K